A surface treatment method for a metal material is provided which includes applying diluted sulfuric acid to a surface of the metal material that is composed primarily of iron, performing a heat treatment on the metal material in the presence of at least one of CO, CO2 and organic gas under nitriding conditions under which a nitrided layer is formed in a superficial layer of the metal material after the application of the diluted sulfuric acid to form a carbon film which includes at least one of carbon nanocoils, carbon nanotubes and carbon nanofilaments on a surface of the nitrided layer of the metal material.