To provide a passage shut-off device quick in response and capable of shutting off a passage in an instant by directly utilizing the abnormal rise of pressure.

This passage shut-off device is composed of a body part 11 provided on the outlet side of the passage and having a blocking seat 13a, and a closing plate 17 movably provided in the body part 11 and normally held being separated from the blocking seat 13a while being moved by a fluid at the abnormal rise of pressure to close the blocking seat 13a. At the abnormal rise of pressure, the closing plate 17 is moved by the fluid itself of high pressure and sonic velocity to close the blocking plate 17, and the closing plate 17 is moved of its own pressure built up by explosion or the like to quicken responsiveness to thereby shut off the passage in an instant. Compared with the case of detecting the pressure rise caused by the explosion or the like, by a sensor and converting it into an electric signal to close a shut-off valve, responsiveness is quick, and dangerous substance can be put in a sealed state without being discharged to the outside.