To provide a structure for preventing a surface layer-forming material from leaking to a back surface side of a base material when a gate is arranged on the PL surface of a mold and injection molding is conducted to the surface of the base material whose margin is arranged in the position opposite to the gate.

The surface layer is molded by arranging the gate on the PL surface of the mold including a fixed mold and a movable mold, arranging the base material on one mold and injection-molding the injection material to the base material surface. In the structure for preventing the injection material from leaking to the back side of the base material in the mold during injection molding, there is mounted in the portion of the placed base material margin opposite to the gate, a protrusion turning to another mold to press the portion of the base material margin opposite to the gate to the mold on which the base material is placed when the molds are closed, or there is mounted in the portion of another mold corresponding to the base material margin, a protrusion turning to the base material.