A tubular body has a vent hole VA and a suction opening. The piston body is in a state in which the inside of the tubular body in an enclosed space is divided into a front chamber and a rear chamber. The piston body includes piston portion which reciprocate in a position on its front end side from the suction opening, a shaft portion which supports this piston portion on its front end side and whose external diameter is smaller than the internal diameter of the tubular body and a pressing portion provided on a rear end side of this shaft portion. A vent passage is formed in the shaft portion so as to couple a vent hole VB of this pressing portion and a vent hole VC on its front end side of the shaft portion. Further, a spring is provided to return the pressed pressing portion to its original position.
