An optical relay apparatus comprising: a first signal converting unit to convert a received optical signal into an electric signal, demodulate and output the electric signal, and modulate an input electric signal in a first modulation scheme and convert the electric signal into an optical signal and transmit the optical signal; and a second signal converting unit to modulate the electric signal output from the first signal converting unit in a second modulation scheme and convert the electric signal into an optical signal and transmit the optical signal, and convert a received optical signal into an electric signal, demodulate the electric signal, and output the electric signal as an electric signal input to the first signal converting unit, characterized in that the optical relay apparatus further comprises an optical switch to perform first switch processing for inputting, to the first signal converting unit, an optical signal output from a first communication station and outputting an optical signal output from the first signal converting unit toward the first communication station and inputting, to the second signal converting unit, an optical signal output from a second communication station and outputting an optical signal output from the second signal converting unit toward the second communication station or second switch processing for inputting, to the first signal converting unit, the optical signal output from the second communication station and outputting the optical signal output from the first signal converting unit toward the second communication station and inputting, to the second signal converting unit, the optical signal output from the first communication station and outputting the optical signal output from the second signal converting unit toward the first communication station. a first signal converting unit to convert a received optical signal into an electric signal, demodulate and output the electric signal, and modulate an input electric signal in a first modulation scheme and convert the electric signal into an optical signal and transmit the optical signal; and a second signal converting unit to modulate the electric signal output from the first signal converting unit in a second modulation scheme and convert the electric signal into an optical signal and transmit the optical signal, and convert a received optical signal into an electric signal, demodulate the electric signal, and output the electric signal as an electric signal input to the first signal converting unit, characterized in that the optical relay apparatus further comprises an optical switch to perform first switch processing for inputting, to the first signal converting unit, an optical signal output from a first communication station and outputting an optical signal output from the first signal converting unit toward the first communication station and inputting, to the second signal converting unit, an optical signal output from a second communication station and outputting an optical signal output from the second signal converting unit toward the second communication station or second switch processing for inputting, to the first signal converting unit, the optical signal output from the second communication station and outputting the optical signal output from the first signal converting unit toward the second communication station and inputting, to the second signal converting unit, the optical signal output from the first communication station and outputting the optical signal output from the second signal converting unit toward the first communication station.