To detect the performance degradation of an optical communication transmission system after it becoming operational, thereby preventing the reliability of the system from lowering. In an optical communication transmission system, one of optical transmitter-receivers in a redundant-structured system is an active optical transmitter-receiver, and the other optical transmitter-receiver is a standby optical transmitter-receiver. The optical transmitter-receiver includes a loopback device through which the signal light of a transmitting section of the optical transmitter-receivers is inputted to a receiving section, and an operating-system switching scheduling device for regularly switching the operating system is provided. Further, there is also provided a performance check scheduling device which operates the loopback device of the standby-system optical transmitter-receiver at a prescribed timing determined in advance to start the performance check processing by the transmitting section and the receiving section of the optical transmitter-receiver.