A movable body that has a cylinder and a valve apparatus is accommodated inside an accommodating chamber of a pump body so as to cover a discharging orifice. A piston sucks a fluid into the movable body, and discharges the fluid from inside the movable body to the discharging orifice by being slid reciprocally through a piston sliding aperture of the cylinder. A relieving passage that communicates between a suction volume space of the accommodating chamber and the discharging orifice is formed between an inner surface of the accommodating chamber and the movable body by the movable body moving away from the discharging orifice in opposition to a force from a forcing body.