To prevent warp deformation without generating sinks and to prevent tracking errors by providing a void part or a foamed part on a thick part at the center part of a thin substrate turned to a high density such as a DVD.

A gaseous body can be injected from a substrate upper surface other than the same gate to which fused resin is injected and filled or a part near it. In this case, in order to prevent the local projection part of the substrate by gas injection port installation, it is preferable to provide a recessed part on a gas injection port part. Since the pressure difference of the inner peripheral part and outer peripheral part of the substrate is suppressed to be extremely small, the warp deformation of the substrate by the nonuniformity of resin filling is made less than the half of a conventional technique. Also, as the result of such low pressure molding, the double refractivity of the substrate is suppressed to be small as well. Further, on the substrate provided with the thick part 10 on the substrate center part, the effect of preventing the sinks of the thick part is provided.