Abstract: A mold 11 having an inner surface coated with a heat insulating film 14 excellent in heat insulation and conformability to a molten resin 20 is clamped with the other mold 12 to form a molding cavity 13. When the molten resin 20 is cooled and solidified in the cavity 13, heat transmission through the mold 11 is suppressed by the film 14 so that a skin layer 23 preferentially grows at the side of the mold 12. Hence, the volumetric shrinkage of the resin 20 during cooling and solidification is selectively absorbed in the deformation of the skin layer 23 separated from the inner surface of the mold 12. As a result, an obtained product has a smooth front surface free from defects such as sink marks. The heat insulating film 14 exhibits the effect to eliminate weld lines, too.