diff --git a/src/main/java/org/ntlab/citrusserver/resources/BooksRest.java b/src/main/java/org/ntlab/citrusserver/resources/BooksRest.java
index 934dc2d..b731b9e 100644
--- a/src/main/java/org/ntlab/citrusserver/resources/BooksRest.java
+++ b/src/main/java/org/ntlab/citrusserver/resources/BooksRest.java
@@ -61,7 +61,13 @@
             throw new WebApplicationException(response.build());
         }
         else{
-            return bookManager.createBook(account_id, title, color, publicity);
+            if (bookManager.createBook(account_id, title, color, publicity) == 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{
+                return bookManager.createBook(account_id, title, color, publicity);
+            }
         }
     }
 
@@ -119,7 +125,7 @@
         }
         else{
             if (bookManager.getTitle(account_id, book_id) == null) {
-                var response = Response.status(Response.Status.FORBIDDEN).entity("アカウントが見つかりません");
+                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{
@@ -161,7 +167,7 @@
         }
         else{
             if (bookManager.getPublicity(account_id, book_id) == null) {
-                var response = Response.status(Response.Status.FORBIDDEN).entity("アカウントが見つかりません");
+                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{