A repeater includes a pump light supplier configured to generate pump light; a first multiplexer configured to multiplex the pump light and a first wavelength division multiplexed optical signal; a second multiplexer configured to multiplex the pump light and a second wavelength division multiplexed optical signal; a first amplifier configured to amplify the first wavelength division multiplexed optical signal by use of the pump light; a second amplifier configured to amplify the second wavelength division multiplexed optical signal by use of the pump light; and a controller configured to control power of the pump light output to the first multiplexer and the second multiplexer, based on wavelength information about at least one of the first wavelength division multiplexed optical signal and the second wavelength division multiplexed optical signal.