To obtain an optical disk substrate having good mechanical characteristics by cooling a resin packed into a die cavity to a uniform temp. at the time of molding a thinly formed optical disk substrate.

The injection molding die for the optical disk substrate is provided with heaters 13b, 23a for heating the portions 31b of the cavity 31 corresponding to the clamping areas of the substrate. Temp. control circuits 12a, 13a, 22a, 24a are disposed in the prescribed positions. Further, the die is provided with a temp. sensor 12b for detecting the temp. of the portion 31a corresponding to the recording region of the substrate in the surface of the cavity 31 and a temp. sensor 13c for detecting the temp. of the portions 31b described above. At the time of molding the substrate, the difference in the surface temps. between the portions 31a and the portion 31b is so controlled as to be kept within 10°.