diff --git a/src/main/java/org/ntlab/citrusserver/resources/AccountsRest.java b/src/main/java/org/ntlab/citrusserver/resources/AccountsRest.java
index 1a430e6..f1ae5e7 100644
--- a/src/main/java/org/ntlab/citrusserver/resources/AccountsRest.java
+++ b/src/main/java/org/ntlab/citrusserver/resources/AccountsRest.java
@@ -46,6 +46,10 @@
     @Consumes(MediaType.APPLICATION_FORM_URLENCODED)//bodyに入力する値がある時
     public String signup(@FormParam("account_id") String accountId, @FormParam("password") String password) {
         String token;
+        if (password == null) {
+            var response = Response.status(Response.Status.BAD_REQUEST).entity("passwordを入力してください");
+            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