PURPOSE: To improve the adhesion between a Ti-N-O film applied on the surface of a substrate and the substrate in a sliding material and to improve its sliding properties, in the thickness direction of the same film, by increasing the oxygen atomic % ratio from the surface of the substrate to the surface of the film.

CONSTITUTION: The surface of the substrate of Fe series, Al series, Ti series or the like is coated with a Ti-N-O film. The oxygen atomic % ratio in this film is increased discontinuously or continuously from the surface of the substrate toward the surface of the film. The range of the thickness of the film is preferably regulated to 1 to 50μm. The range of the Vickers hardness of the film is preferably regulated to 1000 to 2000. This gradient film is formed by increasing the oxygen content introduced within a time from the initial stage of the film forming to the completion of the film forming.