PURPOSE: To provide an amorphous thin film having low frictional coefficient on the surface of steel to be treated by supplying both atmospheric gas and a gaseous compound having Si, O2, C and H2 as a principal component into a vacuum vessel housing the steel to be treated and performing discharge.

CONSTITUTION: Steel 13 to be treated such as high speed steel is placed on a pedestal 12 in a vacuum vessel 11. Gaseous O2 compound such as H2O, gaseous C and H2-based compound such as CH4 and H2-based gas are supplied as a gaseous raw material from an introduction pipe 16 at the rate of (5-50), (5-50) and (5-500) respectively to 1 of gaseous Si compound such as SiCl4 as flow rate ratio. Further, gaseous Ar is supplied as atmospheric gas at the rate of (30-300) to 1 thereof. Discharge is performed between an anode 17 made of stainless steel in the inner wall part of the vacuum vessel 11 and the cathode of the pedestal 12. Thereby, an amorphous thin film shown in Six(Om, Cm, H1-m-n)1-x (wherein x=0.03-0.20, m=0.05-0.5, n=0.1-0.9, 0.6≤m+n≤0.95) is formed on the surface of steel 13. This amorphous thin film has composition of the formula and low frictional coefficient and is large in solid luburicity.