Method for forming surface-treating film

A method for forming a surface-treating film, which comprises applying a film-forming agent onto a metal substrate by a multistage electricity-applying system comprising at least two stages, the method being characterized in that

• (i) the film-forming agent comprises 30-20,000 ppm, in terms of the total amount of metal (as converted to mass), of zirconium compound and, where necessary, a compound containing at least one metal (a) which is selected from titanium, cobalt, vanadium, tungsten, molybdenum, copper, zinc, indium, aluminum, bismuth, yttrium, lanthanide metals, alkali metals and alkaline earth metals, and 1-40% by mass of a resin component,
• (ii) the first stage coating is conducted, with the metal substrate serving as the cathode, by applying electricity at a voltage of 1-50 V (V1) for 10-360 seconds, and the second and subsequent coating is conducted, with the metal substrate serving as the cathode, by applying electricity at a voltage of 50-400 V (V2) for 60-600 seconds, and
• (iii) the difference between the voltage (V2) and the voltage (V1) is at least 10 V.