To provide a safety device that, for preventing an accident due to man-caused misuse, calls attention to a user by issuing an alarm when the user gets away from a gas using site, blocks gas supply after a lapse of a safety time when the user does not become aware of the alarm, can be always closed in nonuse, and can be opened in use.

Detecting the pressure of a gas outflow section and monitoring the using state of a gas range in a gas supply pipe allows a state of an ignition operation/extinguish operation to be independently determined based on the pressure variation and fluctuation of a gas supply pipe without determination by receiving a signal from the gas range. An automatic shut-off valve that is always closed in nonuse and is opened in use is arranged. Also in nonuse of gas, the pressure is monitored, the automatic shut-off valve is opened when the gas pressure becomes a reference value or lower, and the pressure is restored. When the number of restorings becomes a set number or more, gas leakage in the gas supply pipe is determined, and the automatic shut-off valve is locked and blocked.