PURPOSE: To prevent the deposition of unnecessary material on the surface of a structural body made of an aluminum alloy over a long period.

CONSTITUTION: On the tip face of a piston 1 constituted of an aluminum alloy contg. silicon, an intermediate layer 2 is formed. On the intermediate layer 2, a coating layer 3 constituted of fluorocarbon is formed. In this case, since a silicon oxide layer 2a in the intermediate layer 2 covalently bonds with a piston 1 and a transition layer 2b in the intermediate layer 2 covalently bonds with the coating layer 3, the coating layer 3 can firmly bond with the piston 1, and furthermore, since the silicon oxide layer 2a in the intermediate layer 2 is filled into defective parts on the surface of the piston 1, the film bond between the coating layer 3 and piston 1 can moreover be secured. As a result, the peeling of the coating layer 3 from the piston 1 can be prevented, thereby, the generation of cracks on the coating layer 3 can satisfactorily be prevented, thus, the formation of carbon deposits on the surface of the piston 1 can be prevented over a long period.