than the outer diameter of the valve element 41 are directly formed in the passage forming hole 40 a of the bypass passage 40 formed from the discharge passage 33 along the axial direction of the passage forming hole 40 a of the bypass passage 40 and a valve seat face 45 on which the valve element 41 is seated is formed on a portion shifting to the valve port 43 from the valve accommodating hole 44 in a tapered shape such that a diameter of the valve seat face 45 is gradually decreased in this example the valve element 41 is formed of a steel ball and the spring 42 is formed of a compression coil spring the spring 42 is accommodated in and held by the valve port 43 the valve element 41 is accommodated in and held by the valve 2 0 accommodating hole 44 and the valve element 41 is always biased toward a discharge region side a discharge passage 33 side by the spring 42 a stopper member mounting hole 46 which opens at an inner peripheral face of the valve accommodating hole 44 and extends in the direction different from the axial direction of the valve accommodating hole 44 is formed in the vicinity of an opening end.