PURPOSE: To facilitate the disposition of variable throttle to the midway of an oil passage at the discharge side of a hydraulic pump, and thereby eliminate a need for a particular sealing means in a pressure introducing path to the variable throttle by making the revolution axis of planetary gears the rotating shaft of a rotor, and also making a casing stationary.

CONSTITUTION: A vane pump 3 producing hydraulic pressure in response to the difference in revolution between an input shaft 1 and an output shaft 2, that is, the difference in revolution between each front wheel and each rear wheel, and a planetary gear device 4 producing rotation corresponding to the said difference in revolution are disposed within a cylindrical stationary housing 5 the entire surface at one side of which is opened. When there exists the difference in revolution between both of the shafts 1 and 2, the difference in revolution equivalent to the said difference is produced between a sun gear 40 and a ring gear 41, this thereby permits planetary gears 42 and 43 to be revolved around the shaft centers of a bearing mounting plate 44 and a bearing flange 37 while the respective planetary gears rotates around each rotation axis, so that the difference in revolution is thereby absorbed. The rotation of the vane pump 3 is rotated at the sped of the difference in revolution between the sun gear 40 and the ring gear 41 wherein a rotor shaft 36 acts as a revolution axis for the planetary gears 42 and 43.