diff --git a/src/main/java/org/ntlab/citrusserver/repositories/AccountManager.java b/src/main/java/org/ntlab/citrusserver/repositories/AccountManager.java
index bd65aae..602395f 100644
--- a/src/main/java/org/ntlab/citrusserver/repositories/AccountManager.java
+++ b/src/main/java/org/ntlab/citrusserver/repositories/AccountManager.java
@@ -19,14 +19,16 @@
 
     // account_idとpasswordを設定し新しいアカウントを作成する(POST)
     public String createAccount(String accountId, String password) {
-        UUID str = UUID.randomUUID();
-        String token = str.toString();
-        Account account = new Account(accountId, password);
         if(!accounts.containsKey(accountId)) {
+            UUID str = UUID.randomUUID();
+            String token = str.toString();
+            Account account = new Account(accountId, password);
             accounts.put(accountId, account);
             accountToken.put(accountId, token); //accountIDとtokenをHashMapに入れる
+            return token;
+        } else {
+            return null;
         }
-        return token;
     }
 
     //accountIdとtokenを比較してtrueかfalseを返す
diff --git a/src/main/java/org/ntlab/citrusserver/resources/AccountsRest.java b/src/main/java/org/ntlab/citrusserver/resources/AccountsRest.java
index dba0fae..f1ae5e7 100644
--- a/src/main/java/org/ntlab/citrusserver/resources/AccountsRest.java
+++ b/src/main/java/org/ntlab/citrusserver/resources/AccountsRest.java
@@ -51,6 +51,10 @@
             throw new WebApplicationException(response.build());
         }
         token = accountManager.createAccount(accountId, password);
+        if (token == null){
+            var response = Response.status(Response.Status.CONFLICT).entity("id '" + accountId +  "' は既に存在します");//404
+            throw new WebApplicationException(response.build());
+        }
         return token;
     }
 
diff --git a/src/main/java/org/ntlab/citrusserver/resources/BooksRest.java b/src/main/java/org/ntlab/citrusserver/resources/BooksRest.java
index 3398b0b..6e8982c 100644
--- a/src/main/java/org/ntlab/citrusserver/resources/BooksRest.java
+++ b/src/main/java/org/ntlab/citrusserver/resources/BooksRest.java
@@ -39,19 +39,9 @@
     @Produces(MediaType.APPLICATION_JSON)
     public  HashMap<Integer, Book> getBooks(@PathParam("account_id") String account_id, @QueryParam("token") String token){
 
-        if(accountManager.getAccount(account_id) == null){
-            var response = Response.status(Response.Status.NOT_FOUND).entity("アカウントが見つかりません");
-            throw new WebApplicationException(response.build());
-        }
-        else{
-            if(!accountManager.checkToken(account_id, token)) {
-                var response = Response.status(Response.Status.FORBIDDEN).entity("認証失敗");
-                throw new WebApplicationException(response.build());
-            }
-            else{
-                return bookManager.getBooks(account_id);
-            }
-        }
+        accountCheck(account_id);
+        tokenCheck(account_id, token);
+        return bookManager.getBooks(account_id);
     }
 
     @Path("/{account_id}/books")
@@ -60,19 +50,9 @@
     @Consumes(MediaType.APPLICATION_FORM_URLENCODED)  // postmanのbodyに入力する値がある時
     public Book createBook(@PathParam("account_id") String account_id, @FormParam("title") String title, @FormParam("color") String color, @FormParam("publicity") Boolean publicity, @FormParam("token") String token) {
 
-        if (accountManager.getAccount(account_id) == null){
-            var response = Response.status(Response.Status.NOT_FOUND).entity("アカウントが見つかりません");
-            throw new WebApplicationException(response.build());
-        }
-        else{
-            if(!accountManager.checkToken(account_id, token)) {
-                var response = Response.status(Response.Status.FORBIDDEN).entity("認証失敗");
-                throw new WebApplicationException(response.build());
-            }
-            else {
-                return bookManager.createBook(account_id, title, color, publicity);
-            }
-        }
+        accountCheck(account_id);
+        tokenCheck(account_id, token);
+        return bookManager.createBook(account_id, title, color, publicity);
     }
 
 
@@ -83,19 +63,9 @@
     @Produces(MediaType.APPLICATION_JSON)
     public Book getBook(@PathParam("account_id") String account_id, @PathParam("book_id") Integer book_id, @QueryParam("token") String token){
 
-        if (accountManager.getAccount(account_id) == null){
-            var response = Response.status(Response.Status.NOT_FOUND).entity("アカウントが見つかりません");
-            throw new WebApplicationException(response.build());
-        }
-        else{
-            if(!accountManager.checkToken(account_id, token)) {
-                var response = Response.status(Response.Status.FORBIDDEN).entity("認証失敗");
-                throw new WebApplicationException(response.build());
-            }
-            else{
-                return bookManager.getBook(account_id, book_id);
-            }
-        }
+        accountCheck(account_id);
+        tokenCheck(account_id, token);
+        return bookManager.getBook(account_id, book_id);
     }
   /// 本の削除
     @Path("/{account_id}/books/{book_id}")
@@ -104,21 +74,11 @@
     @Consumes(MediaType.APPLICATION_FORM_URLENCODED)
     public String deleteBook(@PathParam("account_id") String account_id, @PathParam("book_id") Integer book_id, @QueryParam("token") String token){
 
-        if(accountManager.getAccount(account_id) == null){
-            var response = Response.status(Response.Status.NOT_FOUND).entity("アカウントが見つかりません");
-            throw new WebApplicationException(response.build());
-        }
-        else{
-            if(!accountManager.checkToken(account_id, token)) {
-                var response = Response.status(Response.Status.FORBIDDEN).entity("認証失敗");
-                throw new WebApplicationException(response.build());
-            }
-            else{
-                todoManager.deleteAllTodosByBookId(account_id, book_id);//削除時、Todoも消す
-                bookManager.deleteBook(account_id, book_id);
-                return "success";
-            }
-        }
+        accountCheck(account_id);
+        tokenCheck(account_id, token);
+        todoManager.deleteAllTodosByBookId(account_id, book_id);//削除時、Todoも消す
+        bookManager.deleteBook(account_id, book_id);
+        return "success";
     }
 
 /// /{account_id}/books/{book_id}/title
@@ -128,19 +88,9 @@
     @Produces(MediaType.TEXT_PLAIN)
     public String getTitle(@PathParam("account_id") String account_id, @PathParam("book_id") Integer book_id, @QueryParam("token") String token){
 
-        if (accountManager.getAccount(account_id) == null) {
-            var response = Response.status(Response.Status.NOT_FOUND).entity("アカウントが見つかりません");
-            throw new WebApplicationException(response.build());
-        }
-        else{
-            if(!accountManager.checkToken(account_id, token)) {
-                var response = Response.status(Response.Status.FORBIDDEN).entity("認証失敗");
-                throw new WebApplicationException(response.build());
-            }
-            else{
-                return bookManager.getTitle(account_id, book_id);
-            }
-        }
+        accountCheck(account_id);
+        tokenCheck(account_id, token);
+        return bookManager.getTitle(account_id, book_id);
     }
 
   /// 本のタイトル変更
@@ -150,20 +100,10 @@
     @Consumes(MediaType.APPLICATION_FORM_URLENCODED)
     public String putTitle(@PathParam("account_id") String account_id, @PathParam("book_id") Integer book_id, @FormParam("title") String title, @FormParam("token") String token){
 
-        if(accountManager.getAccount(account_id) == null){
-            var response = Response.status(Response.Status.NOT_FOUND).entity("アカウントが見つかりません");
-            throw new WebApplicationException(response.build());
-        }
-        else{
-            if(!accountManager.checkToken(account_id, token)) {
-                var response = Response.status(Response.Status.FORBIDDEN).entity("認証失敗");
-                throw new WebApplicationException(response.build());
-            }
-            else{
-                bookManager.putTitle(account_id, book_id, title);
-                return "success";
-            }
-        }
+        accountCheck(account_id);
+        tokenCheck(account_id, token);
+        bookManager.putTitle(account_id, book_id, title);
+        return "success";
     }
 
 /// /accounts/{account_id}/books/{book_id}/public
@@ -173,19 +113,9 @@
     @Produces(MediaType.TEXT_PLAIN)
     public Boolean getPublicity(@PathParam("account_id") String account_id, @PathParam("book_id") Integer book_id, @QueryParam("token") String token){
 
-        if (accountManager.getAccount(account_id) == null) {
-            var response = Response.status(Response.Status.NOT_FOUND).entity("アカウントが見つかりません");
-            throw new WebApplicationException(response.build());
-        }
-        else{
-            if(!accountManager.checkToken(account_id, token)) {
-                var response = Response.status(Response.Status.FORBIDDEN).entity("認証失敗");
-                throw new WebApplicationException(response.build());
-            }
-            else{
-                return bookManager.getPublicity(account_id, book_id);
-            }
-        }
+        accountCheck(account_id);
+        tokenCheck(account_id, token);
+        return bookManager.getPublicity(account_id, book_id);
     }
 
   /// 公開情報を変更する
@@ -195,20 +125,10 @@
     @Consumes(MediaType.APPLICATION_FORM_URLENCODED)
     public String putPublicity(@PathParam("account_id") String account_id, @PathParam("book_id") Integer book_id, @FormParam("publicity") Boolean publicity, @FormParam("token") String token){
 
-        if(accountManager.getAccount(account_id) == null){
-            var response = Response.status(Response.Status.NOT_FOUND).entity("アカウントが見つかりません");
-            throw new WebApplicationException(response.build());
-        }
-        else{
-            if(!accountManager.checkToken(account_id, token)) {
-                var response = Response.status(Response.Status.FORBIDDEN).entity("認証失敗");
-                throw new WebApplicationException(response.build());
-            }
-            else{
-                bookManager.putPublicity(account_id, book_id, publicity);
-                return "success";
-            }
-        }
+        accountCheck(account_id);
+        tokenCheck(account_id, token);
+        bookManager.putPublicity(account_id, book_id, publicity);
+        return "success";
     }
 
 /// /accounts/{account_id}/books/{book_id}/color
@@ -218,24 +138,27 @@
     @Consumes(MediaType.APPLICATION_FORM_URLENCODED)
     public String putColor(@PathParam("account_id") String account_id, @PathParam("book_id") Integer book_id, @FormParam("color") String color, @FormParam("token") String token){
 
-        if(accountManager.getAccount(account_id) == null){
-            var response = Response.status(Response.Status.NOT_FOUND).entity("アカウントが見つかりません");
-            throw new WebApplicationException(response.build());
-        }
-        else{
-            if(!accountManager.checkToken(account_id, token)) {
-                var response = Response.status(Response.Status.FORBIDDEN).entity("認証失敗");
-                throw new WebApplicationException(response.build());
-            }
-            else{
-                bookManager.putColor(account_id, book_id, color);
-                return "success";
-            }
-        }
+        accountCheck(account_id);
+        tokenCheck(account_id, token);
+        bookManager.putColor(account_id, book_id, color);
+        return "success";
     }
 
     ///---------------------------------------------------------------------
     ///private
     ///---------------------------------------------------------------------
 
+    private void accountCheck(String account_id){
+        if(accountManager.getAccount(account_id) == null){
+            var response = Response.status(Response.Status.NOT_FOUND).entity("アカウントが見つかりません");
+            throw new WebApplicationException(response.build());
+        }
+    }
+
+    private void tokenCheck(String account_id, String token){
+        if(!accountManager.checkToken(account_id, token)) {
+            var response = Response.status(Response.Status.FORBIDDEN).entity("認証失敗");
+            throw new WebApplicationException(response.build());
+        }
+    }
 }
\ No newline at end of file
diff --git a/src/main/java/org/ntlab/citrusserver/resources/PublicBooksRest.java b/src/main/java/org/ntlab/citrusserver/resources/PublicBooksRest.java
index 8f5aac4..0ca017f 100644
--- a/src/main/java/org/ntlab/citrusserver/resources/PublicBooksRest.java
+++ b/src/main/java/org/ntlab/citrusserver/resources/PublicBooksRest.java
@@ -27,30 +27,30 @@
     }
 
 
-    //検索条件を指定して本を検索(アカウントかタイトルか両方)
+    //検索条件を指定して本を検索(アカウントかタイトルか両方 ソート可能)
     @Path("/search")
     @GET
     @Produces(MediaType.APPLICATION_JSON)
     public ArrayList<Book> searchBooksByTitleAndAccount(@QueryParam("search_title") String search_title, @QueryParam("search_account_id") String search_account_id,
                                                         @QueryParam("sort_by") Integer sort_by) {
-        if(sort_by == null) {
-            if (search_title != null && search_account_id != null) {
+        if(sort_by == null) { //ソートしない場合
+            if (search_title != null && search_account_id != null) { //タイトルとアカウントIDでの検索
                 return publicBookManager.searchBooksByTitleAndAccount(search_title, search_account_id);
-            } else if (search_title != null) {
+            } else if (search_title != null) { //タイトルのみでの検索
                 return publicBookManager.searchBooksByTitle(search_title);
-            } else if (search_account_id != null) {
+            } else if (search_account_id != null) { //アカウントIDのみでの検索
                 return publicBookManager.searchBooksByAccount(search_account_id);
-            } else {
+            } else { //タイトルもアカウントIDもない場合(すべての本を返す)
                 return publicBookManager.getAllPublicBooks();
             }
-        } else {
-                if(search_title != null && search_account_id != null) {
+        } else { //ソートする場合
+                if(search_title != null && search_account_id != null) { //タイトルとアカウントIDでの検索
                     return publicBookManager.searchBooksByTitleAndAccount(search_title, search_account_id, sort_by);
-                } else if(search_title != null) {
+                } else if(search_title != null) { //タイトルのみでの検索
                     return publicBookManager.searchBooksByTitle(search_title, sort_by);
-                } else if(search_account_id != null) {
+                } else if(search_account_id != null) { //アカウントIDのみでの検索
                     return publicBookManager.searchBooksByAccount(search_account_id, sort_by);
-                } else {
+                } else { //タイトルもアカウントIDもない場合(すべての本を返す)
                     return publicBookManager.getAllPublicBooks();
                 }
             }