In order to improve resolution to the illuminance of light, the present invention comprises a photoelectric conversion circuit for generating a first current in accordance with illuminance of incident light, a charge/discharge circuit whose electrical capacitance changes in accordance with the first current, a first switching element which is turned on or off so as to control conduction between the photoelectric conversion circuit and the charge/discharge circuit, a current circuit for generating a second current with a constant amount, a second switching element which is turned on or off so as to control conduction between the charge/discharge circuit and the current circuit, and a comparator including a first input terminal and a second input terminal, wherein a signal with a reference potential is input to the first input terminal and the second input terminal is electrically connected to the charge/discharge circuit are provided.