PURPOSE: To stabilize reproduction by eliminating defective tracking at the time of the reproduction of a signal recorded into a disk without formation of a distortion of a stamper, by a method wherein molding is performed by pressing the flat stamper against a molding surface of a mold by application of injection molding pressure.

CONSTITUTION: Stampers 12, 12 which are in a flat form are stuck close to molding surfaces of molds 2, 2 as a whole excepting a part of an external circumferential groove 8 and an external circumferential part is supported by an external circumferential ring 18. Synthetic resin is injected through a sprue 30 lying at the center of an inner circumferential holder 28 and streams toward an external circumferential direction within the molds 2, 2. In this instance, the stamper 12 is extended to the external circumference with a flowing force of the synthetic resin and since there is a gap 34, the same is extended to the external circumference without distortion. The stamper 12 is extended at its maximum when the synthetic resin is approached to the external circumferential groove 8. Then the synthetic resin is filled into the mold, pressure within the mold becomes high and the stamper 12 is deformed into a form of the external circumferential groove 8 at a position of the external circumferential groove 8 with synthetic resin pressure.