To increase the retaining performance of lubricating oil in metal surfaces in contact with each other by being subjected to planar pressure, and to reduce the friction coefficient thereof.

Projection materials 29 with a grain size of 10 to 60 μm are projected on a finished face 31 formed on metal surfaces by polishing to form many recessed parts 32 with a depth of 5 to 15 μm on the finished face 31, and a film layer 33 of manganese phosphate composed of manganese phosphate grains 34 with a grain size of 4 to 6 μm is formed on the finished face 31 including the recessed parts 32. Next, the film layer 33 is vanished from the finished face 31 by friction between the surfaces, and the manganese phosphate grains 34 are made to remain inside the recessed parts 32. In this way, lubricating oil supplied to the space between the metal surfaces is retained between the metal surfaces to lubricate the metal surfaces.