The present invention provides an image sensor capable of making waveforms of image signals, which are outputs from photoelectric converting elements, flat, and capable of acquiring image information in high precision. The image sensor includes: a plurality of photoelectric converting elements; a plurality of selecting switches provided in correspondence with the photoelectric converting elements; a scanning circuit for ON/OFF-controlling the selecting switches; a differential amplifier for amplifying a difference voltage between an electric signal entered from the photoelectric converting elements and a reference voltage; and a resistor electrically connected to two input terminals of the differential amplifier.