Abstract: A coating film is formed on the surface of a metal material, wherein the coating film is capable of preventing discoloration due to corrosion of the surface of the metal material even during heat treatment at the time of manufacturing or when used in an outdoor environment over a long period of time, and has an excellent bonding characteristic. A 4 nm to 14 nm thick polysiloxane film, which includes a polysiloxane of which the principal chain is —(Si—O—Si)n— and that is formed by mixing and spraying a hexamethyldisiloxane compound together with nitrogen gas as a carrier gas at atmospheric pressure in a nitrogen plasma gas, and then performing polymerization by radicalizing that hexamethyldisiloxane compound, is formed on the surface of a metal material.