PURPOSE: To obtain stable chipping resistance even in the case of overbaking by irradiating the surface of a composite film after painting and baking with ultraviolet rays when the composite film is formed from a plurality of films before performing painting to form a film.

CONSTITUTION: For example, when a car body is painted, electrodeposition painting 1 is performed as undercoat painting to perform baking 3. Subsequently, the irradiation 5 with UV rays is performed and intercoat painting 7 is performed to perform baking 9. Further, the irradiation 11 with UV rays is performed and topcoat painting 13 is performed to perform baking 15. The baking condition of the baking 3 is usually performed according to a standard baking condition of 170×30min and the baking condition of the bakings 9, 15 is performed according to a standard baking condition of 140°C×30min but, even when the baking temp. of the baking 3 or 9 becomes an over-bake state, stable chipping resistance is obtained. By performing the irradiation with UV rays, a baking condition can be widely set and, therefore, productivity is enhanced and control can be made easy.