In a process for forming a solid lubricating film on an iron-base substrate, an organic material having a vapor pressure of 10.sup.-4 Torr or less at room temperature is deposited on an iron-base alloy substrate in a vacuum atmosphere in a vacuum degree of 10.sup.-4 Torr or more, and simultaneously ions of a metal element having a chemical affinity to carbon is irradiated on the iron-base alloy substrate at a dose of 1.times.10.sup.16 ions/cm.sup.2 or more, the ions having an energy of 5 keV or more. Accordingly, the iron-base substrate is coated with a solid lubricating film which includes an atom mixture layer including carbide of the metal element and alloy of iron and the metal element and a carbon layer including amorphous carbon. Hence, the solid lubricating film has an excellent lubricating property as well as a high adhesion property to the iron-base substrate. Namely, the excellent lubricating property will last for a long period of time.