To prevent rust from being generated on a part when the surface of an object to be coated with a coating is exposed.

A groove 40 is formed on the surface of a portion where a radius of curvature of a spoke 16 shrinks. A part of the coating 38 coating the spoke 16 is deposited on the groove 40. A surface tension acts on the coating 38 in arrow C and arrow D directions parallel to the surface of the spoke 16. Although a coating film on the surface of the portion with a small radius of curvature thins down by action of the surface tension, since the coating 38 is deposited on the groove 40 and the film thickness at the position is ensured, the surface of the spoke 16 is not exposed. Thereby, the generation of the rust on the surface of the portion where the radius of curvature of the spoke 16 shrinks can be suppressed.