PURPOSE: To make the output shaft of a main engine, rotating only in one direction, so as to b rotatable both in the regular and reverse directions by furnishing a differential planetary gearing device on the main engine input shaft, and putting the ring gear and bevel gear of a clutch gear into meshing with the bevel gear and ring gear for joint of the planetary gearing device.

CONSTITUTION: A differential gearing device 2 is installed on the input shaft 1 coupled with the main engine which revolves in one direction. A shaft 7 is installed in the center of a carrier 6 as a bundle of a plurality of planet gears 4, and a bevel gear 10 is installed on this center shaft 7. A ring gear 11 for joint is installed on the cylindrical part 5a of a ring gear 5, and a clutch gear 12 consisting of another bevel gear 13 and ring gear 14 is installed between the first named bevel gear 13 and another ring gear 14 is installed between the first named bevel gear 10 and the said ring gear for joint 11. The clutch gear 12 is mounted on the output shaft 15. If the ring gear 14 of this clutch gear 12 is put in meshing with the bevel gear 10, the input shaft 1 and output shaft 15 rotate in the same direction, and if the bevel gear 13 is meshed with the ring gear 11, the output shaft 15 rotates in the reverse direction.