An optical amplifying repeater is provided which enables even after the main input optical signal is disconnected, the continued returning of a response signal in response to a command signal from an end station. This optical amplifying repeater comprises an optical amplifier, an automatic level control loop including therein a drive control unit, a supervisory unit which returns a response signal RS responding to a command signal CM from an end office, and a detection/control unit which controls the drive control unit so as to increase the amplitude of the response signal RS when a loss of the main optical signal S from an optical transmission line is detected.