PURPOSE: To cure rapidly the synthetic resin material adjacent to a paint bung hole at molding by placing the synthetic resin material of low temperature curing type in the paint injecting portion of a stationary mold, while placing a molding material in the stationary mold.

CONSTITUTION: While the molding material cut into a suitable size is placed in the molding part 1a of a stationary mold 1, the synthetic resin M of low temperature curing type is placed therein. A movable mold 2 is raised at the stage where about 90% of the molding material has been cured, and simultaneously, the paint supplied from a pipe 5 is injected from a nozzle 3, operating a cylinder 4, whereby the paint T is extruded on the surface of a molded product Wa in the molds 1, 2. After the paint has been injected, the movable mold 2 is again clamped on the stationary mold 1, and the paint T is cuased to flow uniformly on the whole surface of the molded product Wa. Then, the molded product Wa and the paint T are cured.