PURPOSE: To output only the output obtained by the photoelectric effect of the light that is made incident on a photoelectric transducer to prevent the saturation of the next stage and also to accurately detect the faint light even when the temperature is high and the light made incident on the photoelectric transducer is intensive.

CONSTITUTION: A current/voltage conversion circuit 3 connected to a photodiode 2 outputs the voltage VA obtained by converting the sum of a supplied dark current and a current acquired by the photoelectric effect to a sampling/holding circuit 5 and a differential amplifier circuit 6. The circuit 5 holds the voltage obtained by converting only the dark current by a sample instruction signal Sd which is outputted from a sample instruction signal output part 4 in a state where no light is made incident on the photodiode 2. When the light is made incident on the photodiode 2, the circuit 6 outputs the voltage obtained by subtracting the voltage held by the circuit 5 from the voltage VA which is outputted from the circuit 3 to an inverse amplifier circuit 7.