An image system uses an amplification-type MOS sensor for receiving an optical image through a photoelectric conversion element, converting the image into an electrical signal, and outputting the signal. This system includes an optical system for guiding this optical image to a predetermined position, an image processing means having a sensor for photoelectrically converting the optical image guided to the predetermined position by the optical system into an electrical signal in units of pixels, and a signal process device for processing an output from the image processing means, and outputting the resultant data. The sensor includes a photoelectric conversion element placed at the predetermined position, an output circuit having an amplification MOS transistor connected to the photoelectric conversion element and serving to amplify and output an output from the photoelectric conversion element at a first timing and output noise independent of the output from the photoelectric conversion element at a second timing, and a noise reduction circuit, connected to the output of the output circuit, having the same impedance at the first and second timings when viewed from the output circuit, and obtaining the difference between outputs from the output circuits at the first and second timings. By setting the same impedance, proper noise cancellation can be performed.