PURPOSE: To enable cancellation of loop islands for the optical repeater provided with a function to exchange data signals with the optical repeater placed opposite to each other.

CONSTITUTION: A delay circuit 18 is provided at the poststage of a signal detecting circuit 111 to detect the existance of a control signal 91 transmitted from the own repeater inside of monitoring control circuits 81 and 82, and a gate circuit 16 is provided at the poststage of a signal detecting circuit 112 to detect the existance of a control signal 92 transmitted from the opposite repeater. Thus, the recognition of the control signal 91 is enabled at the time of transmitting the control signal 91 subsequently even when the control signal 92 is transmitted to the inside of the monitoring control circuit 81, and the cancellation of the loop island can be realized.