Abstract: At the time of closing a die mold, an upper die (18) is rotated with respect to screws (44a-44d) while being brought into contact with a lower die (14) by means of drive gears (42a-42d) and a driven gear (40), wherein a closing force is applied to the material (W) by plate springs (60). Subsequently, at the time of opening the die, under an opposite operation, the upper die (18) is opened while being simultaneously rotated with respect to the screws (44a-44d) which are supported by coil springs (54a-54d), whereby a spiral bevel gear (72) is released from the mold. Accordingly, at the time of die closing, the closing force is kept stable, whereas when the die is opened, imposition of a large force to the gear teeth is prevented, so that bevel gears (72) of high quality and high yield rate can be produced.