Technique for reconnecting office line to key telephone system after power failure

A power failure shunting office line restoring circuit includes: a first relay having an office line tip port connected to a common port for connecting the tip port of the office line to a separate emergency telephone or a key telephone office line accommodating circuit in accordance with a first relay control signal; a second relay having an office line ring port connected to a common port for connecting the ring port of the office line to the emergency telephone or the key telephone office line accommodating circuit in accordance with a second relay control signal; a controller for generating the first and second relay control signals according to a power supply state or emergency telephone use state detection signal; first and second relay drivers for driving the first and second relays in accordance with the first and second relay control signals generated by the controller, and a detector connected to the first relay for detecting the use of the emergency telephone and for outputting the use state detection signal to the controller.