PURPOSE: To prevent excessive fatigue of oil by arranging a changeover valve on one of outlets for immediately returning oil from a corresponding pump for the supplement of high supplement ratio and pressure, and arranging a supply part driving shaft which is connected to independent paired pumps having a common inlet, and is not connected to an outlet.

CONSTITUTION: A driving shaft 10 penetrates rotors of two rotor pumps 12, 14 and is fixed in its angle. A common suctioning passage 16 is connected to both pumps. A passage 24 receives pressure from an outlet 18 which is then applied to a control valve 28 pushed to a closure position by means of a spring 30. At the closure position, a ball valve 32 of a flow passage is opened, and fluid is flowed from the flow passage 22 to an outlet 20 through the flow passage 26. When pressure is increased in the flow passage 18 and exceeds foce of the spring 30, the valve 28 is moved to open the flow passage 22 directly communicated with an oil reservoir. The ball valve is returned to an original position since bidirectional flow between the flow passages 18 and 22 is eliminated.