diff --git a/src/org/ntlab/deltaViewer/CollaborationObjectCallGraph.java b/src/org/ntlab/deltaViewer/CollaborationObjectCallGraph.java
index 6f0b59d..adda005 100644
--- a/src/org/ntlab/deltaViewer/CollaborationObjectCallGraph.java
+++ b/src/org/ntlab/deltaViewer/CollaborationObjectCallGraph.java
@@ -58,8 +58,41 @@
 	 * @param e ExtractedStructure to be merged into the field.
 	 */
 	public void merge(ExtractedStructure e) {
-		references.addAll(e.getDelta().getSrcSide());
-		references.addAll(e.getDelta().getDstSide());
+//		references.addAll(e.getDelta().getSrcSide());
+//		references.addAll(e.getDelta().getDstSide());
+		// Prefer isCreatioin() = true references, if references are equal, but isCreation() is different.
+		for (Reference srcSideRef: e.getDelta().getSrcSide()) {
+			if (references.contains(srcSideRef)) {
+				List<Reference> refs = getReferences(); // Convert to List from Set.
+				int idx = refs.indexOf(srcSideRef);
+				Reference ref = refs.get(idx);
+				if (srcSideRef.isCreation() != ref.isCreation()) {
+					if (srcSideRef.isCreation()) {
+						references.remove(ref);
+						references.add(srcSideRef);
+					}
+				}
+				
+			} else {
+				references.add(srcSideRef);
+			}
+		}
+		for (Reference dstSideRef: e.getDelta().getDstSide()) {
+			if (references.contains(dstSideRef)) {
+				List<Reference> refs = getReferences(); // Convert to List from Set.
+				int idx = refs.indexOf(dstSideRef);
+				Reference ref = refs.get(idx);
+				if (dstSideRef.isCreation() != ref.isCreation()) {
+					if (dstSideRef.isCreation()) {
+						references.remove(ref);
+						references.add(dstSideRef);
+					}
+				}
+				
+			} else {
+				references.add(dstSideRef);
+			}
+		}
 
 		// There may be bug. (Two object has each coordinator like JHotDraw Transform)
 		MethodExecution thisStartPoint = startPoints.get(0);
@@ -149,7 +182,7 @@
 		}
 		System.out.println("replaceCollectionChains: ");
 		for (Reference ref: references) {
-			System.out.println("\t" + ref.getSrcClassName() + "(" + ref.getSrcObjectId() + ")" + " -> " + ref.getDstClassName() + "(" + ref.getDstObjectId() + "): " + ref.isCollection());
+			System.out.println("\t" + ref.getSrcClassName() + "(" + ref.getSrcObjectId() + ")" + " -> " + ref.getDstClassName() + "(" + ref.getDstObjectId() + "): " + ref.isCollection() + ", " + ref.isCreation());
 		}	
 	}