Injection molding of a product and compressive decoration molding of a surface of the molded product are performed using individual cavity molds. A decorative film can be molded efficiently with a thermosetting coating material under suitable temperature control regardless of the shape of the molded product. An injection cavity mold and a decoration cavity mold are employed. The injection cavity mold is set at a hardening temperature of a thermoplastic resin. The decoration cavity mold is set at a thermosetting temperature of a coating material. A molded product is injection-molded in the cavity mold for injection molding and released from the mold. A decorative coating material composed of a liquid thermosetting composition is mounted at least on a part of the top of the injection-molded product. The molded product is located within the cavity mold for decoration molding. A thin decorative film is decoration-molded over the surface of the injection molded product by compression spreading the coating material within the cavity mold for decoration molding over the whole surface to be decorated. The coating material is composed of a liquid thermosetting composition that substantially contains no volatile component having a boiling point below the thermosetting temperature set on the cavity mold for decoration molding.