PURPOSE: To simplify a device by grounding the device through an element which goes to a low impedance for a carrier wave but goes to a high impedance for a commercial power.

CONSTITUTION: The alarm signal outputted form a monitor device 6 is applied to a transmitter TX and is modulated to a carrier wave of, for example, about 2kHz and is applied to electric circuits 1W3 through a transformer T0 connected to an earth wire. In a receiver 5 which receives this signal, a secondary coil is wound around a zero-phase current transformer ZCT which are connected to electric circuits 1W3 to be pierced by them, and this secondary coil is connected to a receiving part RX. The electric circuit 2 is grounded through a capacitor C at a point which is more distant from a receiving transformer T than the receiver 5. The carrier wave applied to electric circuits is flowed through a closed loop formed with the electric circuit 2, the capacitor C, an earth wire 4, and the ground. Thus, the receiver 5 leads out the carrier wave component in the secondary coil of the transformer ZCT connected to the electric wire 2, and various alarm signals are detected in a remote place.