To reinforce an annular groove fitted to a piston ring by forming a reinforcing ring with a sintered body containing a copper base alloy phase, an iron base alloy phase and carbide and having higher hardness than that of a piston body and fixing the reinforcing ring to the piston body, with insert as cast-in through a metallic plating film formed on at least one of the outer surface of the reinforcing ring.

In the sintered body as the reinforcing ring 2, a top ring groove 6 is formed with machining. The reinforcing ring 2 forming the metallic plating film on the side surface, upper surface and bottom surface of the sintered body, is set into a cavity in a metallic mold, and molten aluminum alloy is poured and inserted as cast-in and integrated with a piston base material 1. The surface oxidation of the sintered body is prevented during pouring the molten metal by coating the metallic plating film, and the wetness with the molten aluminum alloy is improved and the film is melted into the molten metal to expose the surface of the sintered body. The sintered body contains by wt.% 10-40 copper base alloy, 0.05-2 carbon, 0.05-1 phosphorus and/or boron and the balance iron base alloy.