By removably disposing a fluid cutoff device in a gas piping, a gas cutoff management function for remote cutting-off/return, etc., can be added to an existing flow measuring unit, and a communicating portion can make bidirectional communications, so that by transmitting an acceptance state of a remote operation from the external device to the external device, higher reliability and safety can be realized, and by detecting use with the fluid cutoff device removed, safety can be further improved while unauthorized use is prevented.