To protect a vacuum pump, a vacuum gauge or the like by suppressing flowing-in of a high pressure gas to a vacuum pump side while allowing suction by the vacuum pump.

An inlet passage (27), a shut-off valve chamber (28) and an outlet passage (29) are successively formed in a valve box (26), and a valve seat (32) is formed in the shut-off valve chamber (28). A shut-off member (33) is advanceably/retreatably inserted into the shut-off valve chamber (28) and is urged to the valve seat (32) side by a gas pressure in the shut-off valve chamber (28). A valve-opening operation chamber (30) is formed in the valve box (26), and a piston member (35) is seal-retainingly and slidably inserted. An atmospheric chamber (36) is formed at one side of the piston member (35), and a negative pressure chamber (37) communicated with the outlet passage (29) is formed at the other side. The piston member (35) is urged by pressure difference of an atmospheric pressure in the atmospheric chamber (36) and a negative pressure in the negative pressure chamber (37). The piston member (35) is cooperated with the shut-off member (33) and when a gas flowing-in from the inlet passage (27) to the shut-off valve chamber (28) is a set pressure or less, the shut-off member (33) is left from the valve seat (32) by movement of the piston member (35).