In a disc molding die, a stationary base plate is attached to a stationary platen, and a stationary mirror-surface plate is attached to the stationary base plate. Further, a movable base plate is attached to a movable platen, and a movable mirror-surface plate is attached to the movable base plate. A stationary guide ring is attached to the stationary base plate so as to surround the stationary mirror-surface plate, while a movable guide ring is attached to the movable base plate so as to surround the movable mirror-surface plate. When the die is clamped, the movable guide ring is brought into contact with the stationary guide ring. A cavity ring is detachably attached to one of the stationary and movable mirror-surface plates such that the cavity ring projects toward the other of the stationary and movable mirror-surface plates. An abutment position adjusting mechanism adjusts the abutment position where the movable guide ring abuts on the stationary guide ring, in accordance with the thickness of the cavity ring. This makes it possible to change the thickness of the cavity without replacing the mirror-surface plates.