diff --git a/src/main/java/org/ntlab/rdlcanvas/parser/StringValue.java b/src/main/java/org/ntlab/rdlcanvas/parser/StringValue.java
index 649b82c..2afdc75 100644
--- a/src/main/java/org/ntlab/rdlcanvas/parser/StringValue.java
+++ b/src/main/java/org/ntlab/rdlcanvas/parser/StringValue.java
@@ -16,6 +16,6 @@
     // 文字列をtoStringメゾットとして返す
     @Override
     public String toString() {
-        return stringValue;
+        return "\"" + stringValue + "\"";
     }
 }