Abstract: An OLT includes an ONU link state monitor that monitors a registered state of each of the ONUs, a continuous light-emission monitor that detects a continuous light-emitting state on the basis of a monitor result given by the ONU link state monitor, and identifies an ONU being in continuous light-emission, and an optical output power shut down command unit that commands the ONU identified by the continuous light-emission monitor to shut down the optical output power. Each of the ONU includes an optical transmitter and receiver device that transmits and receives an optical signal to/from the OLT, and a light output controller that shuts down light of the optical transmitter and receiver device in response to the command given by the optical output power shut down command unit.