diff --git a/src/main/java/org/ntlab/citrusserver/repositories/BookManager.java b/src/main/java/org/ntlab/citrusserver/repositories/BookManager.java
index eb656ad..7185830 100644
--- a/src/main/java/org/ntlab/citrusserver/repositories/BookManager.java
+++ b/src/main/java/org/ntlab/citrusserver/repositories/BookManager.java
@@ -93,6 +93,11 @@
 
     }
 
+    public void deleteAllBooks(String accountId)
+    {
+        booksMap.get(accountId).clear();
+    }
+
     //（（（　目標・振り返りは省略　）））
 
     //本の色を変更する