the a station is set at 34 34 and the polarity of the power supply device of the b station is set at 34 34 to perform power supply then the operation voltage v0 is applied only to the light direct amplifier 9 to make the amplifier operative as a result the optical communication signal fed from the a station is propagated through an optical path reaching the b station through the light distributing coupler 12 1 the light direct amplifier 9 1 the light distributing amplifier 11 1 and through an optical path reaching the b station on the other hand the optical communication signal fed from the b station is propagated through an optical path reaching the a station via the light distributing coupler 11 2 the light direct amplifier 9 2 and the light distributing coupler 12 2 and an optical path reaching the a station it should be noted that in order to operate the circuit of the present invention it becomes necessary to switch the polarity of the power supply device provided for respective terminal stations however since the power supply device should have a function for enabling switching the power supply polarity no problem will arise also since the optical submarine repeater provided at intermediate positions in the optical submarine cable may have a.