To increse the torque of an output side gear and also ensure the usual number of rotation under that torque.

One parts of a gear 8a, 8b, 9a, 9b, 10a, 10b, 11a, 11b are provided on the inner periphery side of the tooth bottom circumference of both sides of the gear 1 and idling tops 2, 3, 4, 5 are installed so as to idle freely and stick to the gear. One parts of the gear 16a, 16b, 17a, 17b, 18a, 18b, 19a, 19b are provided on the outside of the outer periphery of both sides of the respective spindles 12, 13, 14, 15 of the idling tops and driving discs 6, 7 are installed on the both ends of the spindle turnably and a driving source (input shaft) 20 is provided on the disc.