PURPOSE: To facilitate a remote monitoring of the life of a contact point by mounting a highly heat-conductive connecting plate with a temperature sensor mounted thereto which plate is subjected to surface insulating treatment to the terminal plate of a fixed contact, and providing an output circuit connected and disconnected by the output of the temperature sensor and an alarm/display device connected to said circuit.

CONSTITUTION: The PTC thermistor 14a of a detecting device is mounted to a connecting plate 15, which is connected to each terminal plate 3, and the thermistor 14a and a relay unit 16 are connected to each other by a lead wire 17. When main contact points 1, 4 are worn, and the temperature of the main contact points 1, 4 are increased during sending a current to e load 18, this temperature increase is transmitted to the thermistor 14a through the connecting plate 15, and the resistance of the thermistor 14a is increased to reduce its current, so that the relay unit 16 is operated to switch a change-over contact point 16a to the switched contact 16c side. Thus, the current of an electromagnetic coil 10 is broken, and the main contacts 1, 4 are opened. Also, the current is sent to an alarm/display device 24 to light an indication lamp and also operate a buzzer. Hence, the life of the contact point can be easily monitored from a distance.