To provide a MOS type image sensor that can easily obtain information with respect to an illumination light source required for eliminating flicker in an imaged image without the need for provision of a separate detection circuit.

The image sensor employing a sensor circuit for each pixel unit comprising a photoelectric conversion element for producing a sensor current in response to an incident luminous quantity and a transistor for storing electric charges to a parasitic capacitance of the photoelectric conversion element depending on the sensor current and discharging the stored electric charges at an output of the sensor signal, is provided with a means that detects an optical current caused by making light incident into a PN junction of the transistor at storage of the electric charges (at no output of the sensor signal).