To improve the seizure preventiveness of the inner peripheral surface of a cylinder and to smooth the inner peripheral surface of the cylinder by decreasing the number of stages for the surface treatment of the inner peripheral surface of the cylinder and improving the adhesion property of a plating film.

A cylinder block 1 is formed of an aluminum material contg. Si. The anodically oxidized film 3 is formed of an electrolyte consisting of a compd. having a complex forming property and having anion, an org. acid contg. an oxygen acid anion and a halide on the inner peripheral surface 2 of the cylinder. As a result, the number of the stages for the surface transmission of the cylinder is decreased and the adhesion property of the plating film is improved. The halide of the electrolyte may be removed from the anodically oxidized film 3 by selectively dissolving inclusions, such as Si, other additive metals and intermetallic compds. together with the oxygen acid anion.