PURPOSE: To distribute drive power to a plurality of drive shafts by arbitrary ratio with a simple constitution and high responsiveness, by providing a means of changing an initially set load relating to an energizing means of driving a capacity change means in the direction of decreasing a capacity of a variable displacement motor.

CONSTITUTION: In an oil hydraulic motor, each piston 21 of a cylinder block 20 changes a displacement capacity in accordance with a tilt angle α of a swash plate 22, to drive a shaft 23 connected to a rear shaft. When a suction amount of the oil hydraulic motor is small generated relative to a delivery amount of an oil hydraulic pump, for instance, in the case of racing a front wheel with a rear wheel road-held, since a delivery pressure Pd rises, also a pilot pressure Pd applied to a piston 31 of controlling the swash plate 22 is increased, and the piston 31, while increasing the tilt angle α of the swash plate 22 against a spring 30, increases a displacement capacity of the oil hydraulic motor 8. When a solenoid 36 is driven to change an initially set load of the spring 30, a delivery pressure can be arbitrarily set. Accordingly, drive power of a prime mover can be distributed by arbitrary ratio to both the front/rear shafts.