PURPOSE: To remove a hardware constitutional factor to constitute a communication system and the influence of its characteristic by superimposing an address frequency component lower by the quantity of a prescribed value than the frequency band of the data optical signal with the data optical signal transmitted from a terminal station.

CONSTITUTION: A driving circuit 12 for a signal responses to digital data desired to transmit and conduct the driving electric wave of an optical signal correspondence to an emission device 10 in order to output a data optical signal S from the emission device 10. Simultaneously with this driving, the address data of an opponent destination are inputted to a digital/analog conversion circuit (D/A conversion) 14. A voltage from the D/A conversion circuit 14 is impressed to the oscillation control input of a voltage conversion transmitter 16 and the signal of an oscillation frequency of an address data correspondence is generated. The emission device 10 is driven by the driving circuit 18 for an address signal to receive this signal. Consequently, an optical signal to be sent out to an optical fiber cable 20 is superimposed with an address signal (a).