A photodetector is provided, which has the capability of preventing a reduction in dynamic range for a signal light even under a plenty of environmental light to stably obtain a received light output. This photodetector has an accumulation electrode and a holding electrode, which are formed on a photoelectric converting portion through an insulating layer, and a control unit for controlling timings of applying voltages to these electrodes and polarities of the voltages. One of electrons and holes generated in the photoelectric converting portion is accumulated in an accumulation region formed by applying the voltage to the accumulation electrode, and the other is accumulated in a holding region formed by applying the voltage to the holding electrode. Then, the electrons and holes accumulated in the accumulation region and the holding region are recombined, so that remaining electrons or holes not recombined are output.