diff --git a/src/main/java/org/ntlab/citrusserver/entities/Book.java b/src/main/java/org/ntlab/citrusserver/entities/Book.java
index 79039a5..fb612e1 100644
--- a/src/main/java/org/ntlab/citrusserver/entities/Book.java
+++ b/src/main/java/org/ntlab/citrusserver/entities/Book.java
@@ -6,6 +6,7 @@
     private boolean publicity;
     private String color;
     private int bookId;
+    private int todoId = 0;
 
     public void setTitle(String t) {title = t;}
     public String getTitle() {return title;}
@@ -15,4 +16,8 @@
     public String getColor() {return color;}
     public void setBookId(int id) {bookId = id;}
     public int getBookId() {return bookId;}
+    public int getTodoId() {
+        todoId += 1;
+        return todoId;
+    }
 }