A metal mold device for molding a substrate includes a fixed metal mold, a movable metal mold mounted facing the fixed metal mold for being moved towards and away from the fixed metal mold and for defining a mold cavity between it and the fixed metal mold, a stamper mounted on at least one of the fixed metal mold or the movable metal mold and arranged within the mold cavity, a positioning unit provided on the metal mold on which the stamper is mounted for positioning the loading position of the stamper, and a stamper supporting unit provided on the metal mold on which the stamper is mounted for supporting the stamper by suction. The stamper is positioned by the positioning member and held under suction by the stamper suction unit so that it may be mounted in position on the fixed metal mold or the movable metal mold to permit a disc substrate to be molded highly accurately.