To improve the flatness over the entire surface and to set a recording region near to an outer peripheral part by using material having the thermal conductivity smaller than the thermal conductivity of a pair of metal molds for an outer peripheral ring for forming a closed space together with a pair of the metal molds.

At the time of producing the substrate by packing the molten resin material into the cavity 14 formed by a pair of the metal molds 11, 12 and the outer peripheral ring 13 and curing the material, the outer peripheral ring 13 is formed of the material having the thermal conductivity lower than the thermal conductivity of a pair of the metal molds 11, 12 and having the thermal conductivity below 0.03 cal/cm.s.°C. When a pair of the metal molds 11, 12 are formed of a stainless steel, zircon oxide, ceramics, etc., are used for the outer peripheral ring 13. As a result, the cooling rates in the outer peripheral portion and the inner peripheral portion are averaged in the molten resin material and the difference in the shrinkage rate in both portions at the time of curing is relieved and the disk having good flatness is obtd. Then, the setting as the signal recording region near to the outermost periphery is made possible and the increasing of a recording capacity is made possible.