PROBLEM TO BE SOLVED: To provide a surface treatment material having excellent durability and adhesion, to provide a simple method for producing the same by which an environmental load is reduced and cost increase can be suppressed, to provide a body structure of a traffic transportation means, and to provide a body structure of rolling stock.
SOLUTION: The surface treated material 3 is subjected to anticorrosion treatment for suppressing the corrosion in the surface of a magnesium alloy 3a. A carbon layer 3b is a coating layer for coating the magnesium alloy 3a. The diffusion layer 3c is a layer formed by diffusing carbon over the surface of the magnesium alloy 3a. In a state where a carbon material is tightly stuck to the surface of the magnesium alloy 3a, they are heated at 100 to 550°C for 1 to 10 hr, so that carbon is diffused over the magnesium alloy 3a by thermal diffusion reaction to precipitate the diffusion layer 3c consisting of magnesium and carbon over the surface of the magnesium alloy 3a. Thus, the surface of the magnesium alloy 3a is coated with the carbon layer 3b.