diff --git a/Assets/UniGLTF/Runtime/UniGLTF/Format/GltfSerializer.g.cs b/Assets/UniGLTF/Runtime/UniGLTF/Format/GltfSerializer.g.cs
index 7d609c04d..502aec107 100644
--- a/Assets/UniGLTF/Runtime/UniGLTF/Format/GltfSerializer.g.cs
+++ b/Assets/UniGLTF/Runtime/UniGLTF/Format/GltfSerializer.g.cs
@@ -277,9 +277,9 @@ public static void Serialize_gltf_accessors_ITEM(JsonFormatter f, glTFAccessor v
         f.Value(value.bufferView.Value);
     }
 
-    if(value.byteOffset>=0){
+    if(value.byteOffset.HasValue){
         f.Key("byteOffset");
-        f.Value(value.byteOffset);
+        f.Value(value.byteOffset.Value);
     }
 
     if(!string.IsNullOrEmpty(value.type)){
diff --git a/Assets/UniGLTF/Runtime/UniGLTF/Format/glTFBuffer.cs b/Assets/UniGLTF/Runtime/UniGLTF/Format/glTFBuffer.cs
index e153baf7c..99b5b8a4c 100644
--- a/Assets/UniGLTF/Runtime/UniGLTF/Format/glTFBuffer.cs
+++ b/Assets/UniGLTF/Runtime/UniGLTF/Format/glTFBuffer.cs
@@ -96,7 +96,7 @@ namespace UniGLTF
         public int? bufferView;
 
         [JsonSchema(Minimum = 0, Dependencies = new string[] { "bufferView" })]
-        public int byteOffset;
+        public int? byteOffset;
 
         [JsonSchema(Required = true, EnumValues = new object[] { "SCALAR", "VEC2", "VEC3", "VEC4", "MAT2", "MAT3", "MAT4" }, EnumSerializationType = EnumSerializationType.AsString)]
         public string type;
diff --git a/Assets/UniGLTF/Runtime/UniGLTF/IO/ExportingGltfData.cs b/Assets/UniGLTF/Runtime/UniGLTF/IO/ExportingGltfData.cs
index b5d535cc5..1788c7cd1 100644
--- a/Assets/UniGLTF/Runtime/UniGLTF/IO/ExportingGltfData.cs
+++ b/Assets/UniGLTF/Runtime/UniGLTF/IO/ExportingGltfData.cs
@@ -115,7 +115,7 @@ namespace UniGLTF
             var accessorIndex = Gltf.accessors.Count;
             Gltf.accessors.Add(new glTFAccessor
             {
-                byteOffset = 0,
+                byteOffset = default,
                 componentType = glTFExtensions.GetComponentType<T>(),
                 type = glTFExtensions.GetAccessorType<T>(),
                 count = accessorCount,
diff --git a/Assets/UniGLTF/Runtime/UniGLTF/IO/GltfData.cs b/Assets/UniGLTF/Runtime/UniGLTF/IO/GltfData.cs
index 2d1de97b7..6e4feffe4 100644
--- a/Assets/UniGLTF/Runtime/UniGLTF/IO/GltfData.cs
+++ b/Assets/UniGLTF/Runtime/UniGLTF/IO/GltfData.cs
@@ -166,7 +166,7 @@ namespace UniGLTF
         NativeArray<T> GetTypedFromAccessor<T>(glTFAccessor accessor, glTFBufferView view) where T : struct
         {
             var bytes = GetBytesFromBufferView(view);
-            return bytes.GetSubArray(accessor.byteOffset, bytes.Length - accessor.byteOffset).Reinterpret<T>(1).GetSubArray(0, accessor.count);
+            return bytes.GetSubArray(accessor.byteOffset.GetValueOrDefault(), bytes.Length - accessor.byteOffset.GetValueOrDefault()).Reinterpret<T>(1).GetSubArray(0, accessor.count);
         }
 
         /// <summary>
@@ -209,7 +209,7 @@ namespace UniGLTF
         {
             var accessor = GLTF.accessors[accessorIndex];
             var view = GLTF.bufferViews[accessor.bufferView.Value];
-            return GetIntIndicesFromView(view, accessor.count, accessor.byteOffset, accessor.componentType);
+            return GetIntIndicesFromView(view, accessor.count, accessor.byteOffset.GetValueOrDefault(), accessor.componentType);
         }
 
         public NativeArray<T> GetArrayFromAccessor<T>(int accessorIndex) where T : struct
@@ -281,7 +281,7 @@ namespace UniGLTF
             {
                 var view = GLTF.bufferViews[vertexAccessor.bufferView.Value];
                 var segment = GetBytesFromBuffer(view.buffer);
-                result = segment.GetSubArray(view.byteOffset + vertexAccessor.byteOffset, vertexAccessor.count * 4 * vertexAccessor.TypeCount).Reinterpret<float>(1);
+                result = segment.GetSubArray(view.byteOffset + vertexAccessor.byteOffset.GetValueOrDefault(), vertexAccessor.count * 4 * vertexAccessor.TypeCount).Reinterpret<float>(1);
             }
             else
             {
diff --git a/Assets/VRM10/Runtime/IO/Vrm10ImportData.cs b/Assets/VRM10/Runtime/IO/Vrm10ImportData.cs
index 10a6bcd42..c829ffadc 100644
--- a/Assets/VRM10/Runtime/IO/Vrm10ImportData.cs
+++ b/Assets/VRM10/Runtime/IO/Vrm10ImportData.cs
@@ -136,7 +136,7 @@ namespace UniVRM10
                 {
                     var buffer = m_data.Bin;
                     var byteSize = accessor.CalcByteSize();
-                    bytes = m_data.Bin.GetSubArray(view.byteOffset, view.byteLength).GetSubArray(accessor.byteOffset, byteSize);
+                    bytes = m_data.Bin.GetSubArray(view.byteOffset, view.byteLength).GetSubArray(accessor.byteOffset.GetValueOrDefault(), byteSize);
                 }
             }
 
@@ -268,7 +268,7 @@ namespace UniVRM10
                 // IndexBufferが連続して格納されている => Slice でいける
                 var firstAccessor = Gltf.accessors[accessorIndices[0]];
                 var firstView = Gltf.bufferViews[firstAccessor.bufferView.Value];
-                var start = firstView.byteOffset + firstAccessor.byteOffset;
+                var start = firstView.byteOffset + firstAccessor.byteOffset.GetValueOrDefault();
                 if (!firstView.buffer.TryGetValidIndex(Gltf.buffers.Count, out int firstViewBufferIndex))
                 {
                     throw new Exception();
@@ -302,7 +302,7 @@ namespace UniVRM10
                         }
                         var buffer = Gltf.buffers[viewBufferIndex];
                         var bin = GetBufferBytes(buffer);
-                        var start = view.byteOffset + accessor.byteOffset;
+                        var start = view.byteOffset + accessor.byteOffset.GetValueOrDefault();
                         var bytes = bin.GetSubArray(start, accessor.count * accessor.GetStride());
                         var dst = indices.Reinterpret<Int32>(1).GetSubArray(offset, accessor.count);
                         offset += accessor.count;