In order to develop lighter power transmission device, bicycle sprocket was made of CFRP using silicone rubber mold. The filling of the carbon fiber cut into 15mm to the silicone rubber type was excellent In the normal mold method was difficult to control tooth thickness by deformation of mold, but tooth thickness control was possible that using split mold of tooth part. The sprocket made of CFRP of VF25% was made for trial purposes by using the silicone rubber mold There was no problem on teeth though it actually run up to 5000km by installing the sprocket made of CFRP in the bicycle.