diff --git a/src/main/java/org/lastaflute/jta/core/LaTransaction.java b/src/main/java/org/lastaflute/jta/core/LaTransaction.java
index 3172600..8a0ec5b 100644
--- a/src/main/java/org/lastaflute/jta/core/LaTransaction.java
+++ b/src/main/java/org/lastaflute/jta/core/LaTransaction.java
@@ -639,7 +639,7 @@ protected String toCauseHash(Throwable cause) {
     //                                                                      ==============
     @Override
     public String toString() {
-        return xid.toString();
+        return xid != null ? xid.toString() : "(the transaction not initialized yet)";
     }
 
     // ===================================================================================