diff --git a/src/main/java/org/ntlab/acanthus_server/entities/Stroke.java b/src/main/java/org/ntlab/acanthus_server/entities/Stroke.java
index 6e1fecf..b659ccf 100644
--- a/src/main/java/org/ntlab/acanthus_server/entities/Stroke.java
+++ b/src/main/java/org/ntlab/acanthus_server/entities/Stroke.java
@@ -26,8 +26,14 @@
     }
 
     //座標のリストを返す
-    public SortedSet<Position> getPositions() {
-        return this.positions;
+    public List<Position> getPositions() {
+
+        List<Position> positions = new ArrayList();
+        for (Position p: positions) {
+            positions.add(p);
+        }
+
+        return positions;
     }
 
     // StrokesRestからstrokesのsizeをもらってstrokeNoに入れる