To solve the problem that a flawless coating excellent in adhesion to a metallic conductor is conventionally difficult to form due to the effect of the oxide layer or surface-treated layer of the conductor surface, when a polymer film is formed on the metallic conductor by electrolytic polymerization to coat the conductor.

Electrolysis is conducted with the metallic conductor as an anode to oxidize and dissolve the conductor, then electrolysis is performed with the oxidized and dissolved conductor as a working electrode in an aqueous solution containing a polymerizable monomer, a supporting electrolyte and an alkylamine to form a polymer film on the conductor, and the conductor is coated.