A photoelectric conversion device includes a pixel that outputs a pixel signal in accordance with an incident light, a plurality of signal holding units each configured to hold the pixel signal, an AD conversion unit that converts the pixel signal from analog signal to digital signal, a first switch circuit provided between the pixel and the plurality of signal holding units, and a second switch circuit provided between the plurality of signal holding units and the AD conversion unit. The first switch circuit is configured to connect the pixels to the plurality of signal holding units individually to hold one pixel signal in the plurality of signal holding units, respectively, in different sampling periods, the second switch circuit is configured to switch connection between the plurality of signal holding units and the AD conversion unit, and pixel signals held in the plurality of signal holding units are averaged and output.