diff --git a/Assets/VRM10/Runtime/Components/Vrm10Instance/Vrm10Instance.cs b/Assets/VRM10/Runtime/Components/Vrm10Instance/Vrm10Instance.cs
index d6b1afdde..daee18e60 100644
--- a/Assets/VRM10/Runtime/Components/Vrm10Instance/Vrm10Instance.cs
+++ b/Assets/VRM10/Runtime/Components/Vrm10Instance/Vrm10Instance.cs
@@ -68,7 +68,8 @@ namespace UniVRM10
 
         private UniHumanoid.Humanoid m_humanoid;
         private Vrm10Runtime m_runtime;
-        public IVrm10SpringBoneRuntime m_springBoneRuntime { get; set; }
+        // 中継用。InitializeAtRuntime でもらって MakeRuntime で使う
+        IVrm10SpringBoneRuntime m_springBoneRuntime;
         private IReadOnlyDictionary<Transform, TransformState> m_defaultTransformStates;
 
         /// <summary>
@@ -114,7 +115,7 @@ namespace UniVRM10
             }
         }
 
-        public Vrm10Runtime MakeRuntime(bool useControlRig)
+        internal Vrm10Runtime MakeRuntime(bool useControlRig)
         {
             return new Vrm10Runtime(this, useControlRig, m_springBoneRuntime);
         }
diff --git a/Assets/VRM10/Runtime/IO/IVrm10SpringBoneRuntime.cs b/Assets/VRM10/Runtime/IO/IVrm10SpringBoneRuntime.cs
index e514823ce..4ed48cb4f 100644
--- a/Assets/VRM10/Runtime/IO/IVrm10SpringBoneRuntime.cs
+++ b/Assets/VRM10/Runtime/IO/IVrm10SpringBoneRuntime.cs
@@ -28,7 +28,8 @@ namespace UniVRM10
         public Vector3 ExternalForce { get; set; }
 
         /// <summary>
-        /// SpringBone を一時停止する
+        // SpringBone のランタイムの動作状態を設定する。
+        // SpringBone の動きを一時停止したいときは false にする。
         /// </summary>
         public bool IsSpringBoneEnabled { get; set; }