The pump housing, the rotor which is rotatably arranged inside the pump housing and, the outer ring, and the spring member are included. As to the pump housing, the suction port and the discharge port in which oil is the exit and entrance are formed and the chamber supplying oil is built up. As to the rotor which is rotatably arranged inside the pump, multiple vanes are installed. As to the outer ring, the insertion part in which the rotor is rotated is formed in the inside and the oil pocket in which one side is made eccentric within the pump housing about the center of the rotor and which is installed rotatably and which is formed at the interval of the inner wall surface of the outer periphery of the rotor and insertion part with the vane is formed. The spring member is installed between the outer ring and pump housing and elastically supports the installation state made eccentric of the outer ring. Here, in the position in which the suction port and discharge port are separated in each other, it is formed as the inside of the pump housing at the lower part of the rotor and the depth of one part of the discharge port can be formed into the depth corresponding to the thickness of the rotor.