In an optical receiver, a light receiving element receives the optical packet signals and converts the optical packet signals to electrical signals. A bias voltage supply section supplies bias voltage to the light receiving element. A monitoring section monitors an input level of each optical packet signal or each electrical signal and transmits a monitored value to the bias voltage supply section. In addition, the bias voltage supply section temporarily increases the bias voltage according to magnitude of the monitored value after an end of receiving of each optical packet signal.