PURPOSE: To mold disc boards of different size using a single main die without replacing the die entirely.

CONSTITUTION: A mirror block 17 is fixed through a fixing bolt 27 to a fixed plate 15 thus forming a fixed die 7 while a mirror block 51 is fixed through a fixing bolt 59 to a movable plate 50 thus forming a movable die 8. An inner peripheral stopper 21 is held by a holder 37 while an outer peripheral stopper ring 22 is held by a holder 44 thus securing a stamper 9 to the fixed die 7. The mirror blocks 17, 51 and the outer peripheral stopper ring 21 for the fixed die 7 and the movable die 8 are prepared depending on the stamper 9 for a disc board to be molded and they are replaced by removing the fixing bolts 27, 59 and the outer peripheral stopper ring 22. The outer peripheral stopper ring 22 is held by the holder when it is turned under closed state.