diff --git a/src/main/java/org/ntlab/citrusserver/repositories/AccountManager.java b/src/main/java/org/ntlab/citrusserver/repositories/AccountManager.java
index e2a9ca0..751131f 100644
--- a/src/main/java/org/ntlab/citrusserver/repositories/AccountManager.java
+++ b/src/main/java/org/ntlab/citrusserver/repositories/AccountManager.java
@@ -93,7 +93,10 @@
 
     // 指定されたIDの自己紹介を返す(GET)
     public String AccountIntro(String accountId) {
-        return accounts.get(accountId).getIntroduction();
+        if(accounts.containsKey(accountId)) { //アカウントがあるかを確認
+            return accounts.get(accountId).getIntroduction();
+        }
+        return null;
     }
 
     // 指定されたIDの自己紹介を変更する (PUT)