A surface-treated steel material having cut edge corrosion resistance that is equal to or more than that of a chromate treatment without use of hexavalent chromium. The surface-treated steel material includes a coating film formed on a surface of a steel material through a plating layer that is obtained by immersing the steel material in a galvalume bath containing Mg. The coating film is formed using a coating composition containing a coating film-forming resin, a cross-linking agent, a predetermined vanadium compound, and trimagnesium phosphate; the vanadium compound is a compound satisfying a predetermined electrical conductivity; the content of the vanadium compound is restricted to a predetermined amount; the vanadium compound satisfies a predetermined pH; and the content of the trimagnesium phosphate is a predetermined amount.