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
diff --git a/src/main/java/org/ntlab/acanthus_server/resources/gallery/StrokesRest.java b/src/main/java/org/ntlab/acanthus_server/resources/gallery/StrokesRest.java
index 0276096..c426591 100644
--- a/src/main/java/org/ntlab/acanthus_server/resources/gallery/StrokesRest.java
+++ b/src/main/java/org/ntlab/acanthus_server/resources/gallery/StrokesRest.java
@@ -197,7 +197,7 @@
     @Path("/{aid}/pageMap/{pid}/layers/{layerNo}/strokes/{strokeNo}/positions")
     @GET
     @Produces(MediaType.APPLICATION_JSON)
-    public SortedSet<Position> getPositions(@PathParam("aid") Integer aid, @PathParam("pid") Integer pid,
+    public List<Position> getPositions(@PathParam("aid") Integer aid, @PathParam("pid") Integer pid,
                                             @PathParam("layerNo") Integer layerNo, @PathParam("strokeNo") Integer strokeNo) {
         var pages = gallery.getAnimationByAid(aid).getPages();
         var strokes = new ArrayList<Stroke>();