Fluid inlet and outlet portions are provided for introducing and discharging a hydraulic fluid. The fluid outlet portion includes a plurality of outlet ports. A drive shaft is provided that rotates about its axis. A plurality of volume variable pump chambers are arranged about the drive shaft and rotated by the same. The pump chambers are arranged between the fluid inlet and outlet portions for compressing the hydraulic fluid from the fluid inlet portion before discharging the same from the fluid outlet portion. The pump chambers are exposed to the outlet ports separately one after another when the pump chambers are rotated by the drive shaft. A discharge rate varying mechanism is provided that varies a fluid discharge rate of each of the outlet ports by varying the amount of the fluid led to the outlet ports.