An optical communication system, where in an optical transmission apparatus arranged on a transmission side of respective repeating sections, an OSC optical amplifier is provided on an OSC light optical path between from an OSC transmitter to a multiplexer, and the OSC optical amplifier is controlled so that the power of OSC light transmitted on the transmission path becomes a previously set target value. As a result the OSC light is amplified by a different amplifying device to that for the main signal lights at the time of transmission. Therefore even in the case where the span losses are large, OSC light can be reliably received by the optical transmission apparatus on the reception side.