A low-cost optical current monitor circuit that converts optical current output signals from a plurality of photodiodes (PD1 to PDn) into the voltage signal for monitoring. The optical current monitor circuit has a multiplexer circuit (MUX) that selects one of the input terminals, to which each of the photodiodes (PD1 to PDn) is connected, for connection with the output terminal, and an amplifier (LA) that converts the optical current signal flowing from the selected photodiode via the multiplexer circuit (MUX) into the voltage output signal.
