To provide mechanical security system which minimizes security bland time and non-security state and improve operating efficiency of the mechanical security system.

This system is constituted by an alarm to which a sensor for putting out a detection signal when abnormality in a monitored zone is detected and a guard switching means 11 for switching the monitored zone to the guard state or the guard-cancelled state are connected, and a monitor center device 20 provided at a monitor center for remotely monitoring the monitored zone, the alarm device 10 has a manipulating means 12 requiring manipulation to put the sensor 16 not putting out a detection signal even when some of the sensors 16 in the sensors 16 issue a detection signal, and when the guard switching means 11 is manipulated after the manipulating means 12 is manipulated, it sends a guard defective signal of the monitor center device 20.