PURPOSE: To efficiently and easily form a thin composite nitride film having superior wear resistance and electric insulating property by simultaneously evaporating B and Si or Al and Ti under controlled condition and reacting generated vapors with gaseous nitrogen.

CONSTITUTION: A cleaned substrate is subjected to ion bombardment in an Ar atmosphere or the like in an ion plating chamber to carry out further cleaning by electric discharge. Gaseous N2 as a reactive gas is then introduced into the chamber, B and Si sources or Al and Ti sources in the chamber are irradiated with electron beams to simultaneously generate vapors of the two kinds of metals and reactive ion plating is carried out. The compounding ratio between the two kinds of metals is controlled by regulating the amt. of electron beams for irradiation. Thus, an arbitrary compsn. is accurately obtd. and a thin composite nitride film having superior characteristics is formed on the substrate.