PURPOSE: To use the same circuit for both the supply of power and transmission of information by connecting a capacitor between a pair of circuits which connects a transmitter and a receiver to transfer the power supply at both ends of the capacitor and at the same time providing a transformer having its secondary winding connected in series to a circuit from the juncture of the capacitor.

CONSTITUTION: A transmitting/receiving device 1 of the power supply side is connected to a commercial power supply and transmits and receives the power supply and information signals to other transmitting/receiving devices from terminals 4a and 4b via a secondary winding 6b of a transformer 6. Only the component of a power supply VB emerges at both ends of a capacitor 8 connected in parallel to both ends 7a and 7b of a power supply VB. While only the information component emerges at both ends of the winding 6b. These two components can be separated from each other. The information signal delivered from the terminal OUT of a transmitting/receiving logical circuit 13 is modulated by a modulating circuit 11 and transmitted via the transformer 6. The signal transmitted through circuits 5a and 5b undergoes wave detection through a demodulating circuit 12 via the transformer 6.