PURPOSE: To simplify the construction, miniaturize the device, and reduce the weight by providing two set of differential gears on a driving force transmitting route, providing respective differential gears on prescribed positions concerning to three wheels, and additionally providing a differential limiting mechanism to limit differential movement of front wheels and rear wheels.

CONSTITUTION: Two set of planetary gear mechanisms 30, 40 and an input gear 18 are provided side by side in series around front wheel drive shafts 10a, 10b, and a one body type differential 14 is constituted out of them 30, 40, 18. Driving force transmitted from the input gear 18 to the carrier 32 of the planetary gear mechanism 30 is distributed to a ring gear 36 and a sun gear 38 through a planet gears 34, the driving force distributed to the sun gear 38 is transmitted to the left front wheel drive shaft 10a. Meanwhile, the driving force distributed to the ring gear 36 is transmitted to the carrier 42 of the planetary gear mechanism 40, and transmitted to a ring gear 46 and a sun gear 48. The driving force transmitted to the sun gear 48 is transmitted to the right front wheel drive shaft 10b, and the driving force transmitted to the ring gear 46 is transmitted to rear wheel drive shafts 27a, 27b.