PURPOSE: To raise durability strength by arranging a masking member for preventing shot grains from being projected into a V-groove formed on the surface side of a part fitting the rim member to the disk member between a rim member and a disk member and shot-peening the disk member.

CONSTITUTION: The steel rim member 1 and the steel disk member 2 are formed respectively independently, fitted to each other and joined by welding 3. The masking member 6 is arranged in the V-groove 4 formed on the surface of this joined part. The masking member 6 is made from material rich in durability such as rubber, resin, metal, etc. The shots are projected by the shot peening method like arrows A, B. The shot grains are not projected into the V-groove 4 and do not remain in the V-groove. Then, the masking member is taken out of the V-groove 4 and coated with rust preventive coating material, etc. In this way, the durability strength of the disk part is raised and the durability of a steel road wheel can be improved at a large width.