<p>A hollow section (52a) for embedding a discharge check valve (70) into a piston (50) configured from a piston main body (52) and a shaft part (54) extends from the tip end surface of the piston (50) to the middle of the interior of the shaft part (54) by penetrating the interior of the piston main body (52) at the axial center. As a consequence it is possible to embed the discharge check valve (70) into the piston (50) even when the length of the piston (50) is the bare minimum. Moreover, it is possible to bring the discharge port (43) into communication with the hollow section (52a) of the piston (50) by simply forming through-holes (54a, 54b) on the shaft part (54) in the radial direction, thereby being able to facilitate processing.</p>
