quantity the spool 44 is moved further by the operation of the metering orifice 51 to sequentially connect these second discharge passages 36 and 37 with the suction passages 32 and 33 as a consequence a portion of the pressurized oil is returned to the tank thus maintaining the quantity of the pressurized oil supplied through the discharge passage 50 below the predetermined value although in the foregoing embodiment the flow control valve 40 having a flow path transfer function of sequentially connecting the first and second discharge passages 34 35 36 37 to the suction passages and a flow quantity control function of controlling the pressurized oil flowing between the first and second discharge passages and the suction passages is arranged coaxially with the drive shaft 20 of the rotor in the rear body 16 the invention is not limited to this construction it is only necessary to efficiently arrange the suction passages and the first and second discharge passages in the rear body it is also possible to reversely position the spool 44 in the flow control valve 40 to make the side of the plug 43 as the high pressure chamber the positions of the openings of various passages may be selected correspondingly conversely the first discharge passages may be connected to passage 50 to which the second discharge passages may be connected through check valves the discharge passage 50 and the connector 53 on the discharge side are not always necessary to be arranged in the axial direction of the rear body 16 they can be disposed at.