A rear frame is formed of a laminate that includes a plurality of carbon fiber layers laminated one on top of another and hardened and integrated with each other by a plastic. A different color layer having a color different from a color of the carbon fiber layers is disposed between the carbon fiber layers in the laminate. When a carbon fiber layer on the outside is lost by a piece of flying gravel and a lost portion reaches the different color layer, a surface of the different color layer is exposed from the lost portion. An exposed portion having the different color can be easily recognized from the outside. The appearance of the exposed portion allows arrival of a replacement time of the rear frame to be recognized. As a result, it is possible to enable easy visual recognition of an optimum replacement timing.