diff --git a/Assets/VRM10/Editor/Vrm10InstanceEditor.cs b/Assets/VRM10/Editor/Vrm10InstanceEditor.cs
index b01285417..8a57829f4 100644
--- a/Assets/VRM10/Editor/Vrm10InstanceEditor.cs
+++ b/Assets/VRM10/Editor/Vrm10InstanceEditor.cs
@@ -188,8 +188,10 @@ namespace UniVRM10
                 {
                     if (instance.TryGetBoneTransform(HumanBodyBones.LeftThumbDistal, out var l2))
                     {
-                        var color = new Color(1.0f, 0.5f, 0.5f, 0.8f);
-                        DrawThumbGuide(Vector3.up, color, l0, l1, l2);
+                        var color = new Color(0.5f, 1.0f, 0.0f, 1.0f);
+                        var thumbDir = (Vector3.forward + Vector3.left).normalized;
+                        var nailNormal = (Vector3.forward + Vector3.right).normalized;
+                        DrawThumbGuide(l0.position, l2.position, thumbDir, nailNormal, color);
                     }
                 }
             }
@@ -199,24 +201,62 @@ namespace UniVRM10
                 {
                     if (instance.TryGetBoneTransform(HumanBodyBones.RightThumbDistal, out var r2))
                     {
-                        var color = new Color(0.5f, 0.5f, 1.0f, 0.8f);
-                        DrawThumbGuide(Vector3.down, color, r0, r1, r2);
+                        var color = new Color(0.5f, 1.0f, 0.0f, 1.0f);
+                        var thumbDir = (Vector3.forward + Vector3.right).normalized;
+                        var nailNormal = (Vector3.forward + Vector3.left).normalized;
+                        DrawThumbGuide(r0.position, r2.position, thumbDir, nailNormal, color);
                     }
                 }
             }
         }
-        static void DrawThumbGuide(Vector3 up, Color color, Transform t0, Transform t1, Transform t2)
+        static void DrawThumbGuide(Vector3 metacarpalPos, Vector3 distalPos, Vector3 thumbDir, Vector3 nailNormal, Color color)
         {
             Handles.color = color;
             Handles.matrix = Matrix4x4.identity;
-            var len = (t0.position - t1.position).magnitude;
-            var dir0 = (t0.position - t1.position).normalized;
-            var dir2 = (t2.position - t1.position).normalized;
-            var angle = Mathf.Acos(Vector3.Dot(dir0, dir2)) * Mathf.Rad2Deg;
-            Handles.DrawSolidArc(t1.position, up, dir0, angle, len);
-            Handles.color = Color.green;
-            Handles.DrawLine(t1.position, t1.position + Vector3.up * len);
-            Handles.Label(t1.position, "thumb guide");
+
+            var thumbVector = distalPos - metacarpalPos;
+            var thumbLength = thumbVector.magnitude * 1.5f;
+            var thickness = thumbLength * 0.1f;
+            var tipCenter = metacarpalPos + thumbDir * (thumbLength - thickness);
+            var crossVector = Vector3.Cross(thumbDir, nailNormal);
+
+            // 指の形を描く
+            Handles.DrawLine(metacarpalPos + crossVector * thickness, tipCenter + crossVector * thickness);
+            Handles.DrawLine(metacarpalPos - crossVector * thickness, tipCenter - crossVector * thickness);
+            Handles.DrawWireArc(tipCenter, nailNormal, crossVector, 180f, thickness);
+
+            Handles.DrawLine(metacarpalPos + nailNormal * thickness, tipCenter + nailNormal * thickness);
+            Handles.DrawLine(metacarpalPos - nailNormal * thickness, tipCenter - nailNormal * thickness);
+            Handles.DrawWireArc(tipCenter, crossVector, -nailNormal, 180f, thickness);
+
+            Handles.DrawWireDisc(metacarpalPos, thumbDir, thickness);
+            Handles.DrawWireDisc(tipCenter, thumbDir, thickness);
+
+            // 爪の方向に伸びる線を描く
+            Handles.DrawDottedLine(tipCenter, tipCenter + nailNormal * thickness * 8.0f, 1.0f);
+
+            // 爪を描く
+            Vector2[] points2 = {
+                new Vector2(-0.2f, -0.5f),
+                new Vector2(0.2f, -0.5f),
+                new Vector2(0.5f, -0.3f),
+                new Vector2(0.5f, 0.3f),
+                new Vector2(0.2f, 0.5f),
+                new Vector2(-0.2f, 0.5f),
+                new Vector2(-0.5f, 0.3f),
+                new Vector2(-0.5f, -0.3f),
+                new Vector2(-0.2f, -0.5f),
+            };
+            Vector3[] points = points2
+                .Select(v => tipCenter + (nailNormal + crossVector * v.x + thumbDir * v.y) * thickness)
+                .ToArray();
+
+            Handles.DrawAAPolyLine(points);
+            Handles.color = color * new Color(1.0f, 1.0f, 1.0f, 0.1f);
+            Handles.DrawAAConvexPolygon(points);
+
+            // 文字ラベルを描く
+            Handles.Label(tipCenter + nailNormal * thickness * 6.0f, "Thumb nail direction");
         }
     }
 }