PURPOSE: To obtain a hardened surface layer without any clear boundary with a substrate and excellent in adhesion and wear resistance by irradiating the substrate surface with N ion while vapor-depositing a metal on the surface and reducing the concn. of the nitride formed from the surface toward the inside.

CONSTITUTION: An ion source 5 for irradiating a water-cooled rotary substrate holder 3 with N ion 4 from an angle of 45° and a source 7 for Ti vapor 6 are provided in a chamber 2 evacuated by a vacuum pump 1. The surface of a substrate 8 is irradiated with an N ion beam 4 while vapor-depositing Ti on the surface to form a Ti film on the substrate 8 surface. In this case, the TiN concn. is reduced from the substrate 8 surface toward the inside, and the ratio of the characteristic values by X-ray diffraction from the (200) and (111) faces of the TiN (I200/I111) is set to ≤1.0. Consequently, the obtained surface layer has the above-mentioned characteristics, the hardness is drastically improved, and the method is more effectively applied to an Al alloy, etc., since the alloy is treated especially at low temp.