diff --git a/src/main/java/org/ntlab/citrusserver/repositories/FavoriteManager.java b/src/main/java/org/ntlab/citrusserver/repositories/FavoriteManager.java
index 9452ca7..48603ad 100644
--- a/src/main/java/org/ntlab/citrusserver/repositories/FavoriteManager.java
+++ b/src/main/java/org/ntlab/citrusserver/repositories/FavoriteManager.java
@@ -130,10 +130,12 @@
 
     // bookIdを削除したいとき
     public void removeFavoriteByBookID(String accountId, Integer bookId) {  // accountIdはamika1107
-        for (String otherAccountId : favoritedMap.get(accountId).get(bookId)){
-            favoritesMap.get(otherAccountId).get(accountId).remove(bookId); // tesのbookId を削除
+        if(favoritedMap.containsKey(accountId) && favoritedMap.get(accountId).containsKey(bookId)) {
+            for (String otherAccountId : favoritedMap.get(accountId).get(bookId)){
+                favoritesMap.get(otherAccountId).get(accountId).remove(bookId); // tesのbookId を削除
+            }
+            favoritedMap.get(accountId).remove(bookId);  // tedのbookIdを消したいとき
         }
-        favoritedMap.get(accountId).remove(bookId);  // tedのbookIdを消したいとき
     }
 
     @Override