A valve member having a valve part and a piston part is accommodated in a piston accommodation cylinder part of a case reciprocatably, and a damper chamber that is substantially a sealed space is formed in an anti-valve seat side in the valve member so that fluid flows without flowing via the damper chamber. Accordingly, since the fluid does not pass through the damper chamber, a fluid force that occurs in the piston part due to a fluid flow does not change easily, thus it becomes difficult to increase hunting at the valve members. Moreover, in a vibrational component in the valve member reciprocating direction of the valve members, amplitude of the vibration can be decreased by a damping force generated in the damper chamber.