A photoelectric current integrating circuit including: a first operational amplifier with a switch and an integrating capacitor connected in parallel between an input terminal and an output terminal thereof; a photodiode; and a current passing circuit provided between one terminal of the photodiode and the input terminal of the first operational amplifier, for passing a photoelectric current detected at the photodiode while blocking a connection between a parasitic capacitance of the photodiode and the integrating capacitor.