PURPOSE: To improve the performance of the pump, miniaturize the size and reduce the weight thereof by a method wherein leaking fluid, reserved in the oil seal part of a rotor rotating shaft, is introduced into the suction side of the pump which never affect to a flow amount control valve or the like.

CONSTITUTION: A front body 11 which forms a pump body, a rotor 13, a cam 14 and a side plate 32 arranged at one side of the ring 14 are accommodated in an assembled condition. A pump accommodating space 31, forming a pump delivery side pressure chamber 21 at the bottom side thereof between the side plate 32, is provided. A groove 48, connected to the oil seal part 47 at the outer end side of the rotating shaft 18 of the rotor 13 through a passing hole 49, is provided at one part of the inner periphery of the pump accommodating space 31 and is connected to a pump suction side 19 through the groove 50 of path formed on the side plate 32. According to this method, the leaking liquid, reserved in the oil seal part 47, may be introduced into the pump suction side 19 which will never affect to the flow amount control valve 17 or the like and, thus, the performance of the pump may be improved and the miniaturization as well as the reduction of weight of the pump may be contributed by this method.