A method for coating a metal substrate in which a coating film is applied reliably and strongly on a surface processed film on a metal matrix material. The coating method for the metal substrate includes an immersion step of immersing a surface-processed metal substrate in a solution mainly composed of an amorphous-like fluorine resin, a polymerization step of polymerizing the amorphous-like fluorine resin and the surface processed metal substrate, and a step of forming a coating film on a surface-processed surface of the metal substrate.