The present disclosure includes a photodetector element (11) that converts an optical signal into an electric current signal; a transimpedance amplifier (12a) that converts the electric current signal into a voltage signal; a differential amplifier (12d) that converts the voltage signal into a differential signal, by performing differential amplification of a difference between the voltage signal and a threshold voltage; an LOS detection circuit that detects a no-signal section of the optical signal; and an MCU that repeatedly executes offset cancellation processing, the offset cancellation processing including threshold voltage change processing in which the threshold voltage is changed such that an offset voltage of the differential signal is reduced, the MCU 13 skipping the threshold voltage change processing in the no-signal section.