An imaging device comprises a pixel array, a reading unit, a pixel signal addition unit, and a display unit. A plurality of pixels including a first pixel and a second pixel are arranged in two dimensions in the pixel array. The first and second pixels have a photoelectric conversion elements and output pixel signals according to the quantities of incident light to the photoelectric conversion elements. The reading unit reads a first pixel signal from the first pixel and reads a second pixel signal from the second pixel. The pixel signal addition unit adds the first pixel signal read from the first pixel with a plurality of different timings and adds the second pixel signal read from the second pixel with a plurality of different timings. The display unit displays the first pixel signal added by the pixel signal addition unit and the second pixel signal added by the pixel signal addition unit sequentially with different timings.