A photoelectric conversion device comprising a pixel portion in which pixels each including a photoelectric converter are arranged, a sample/hold unit configured to sample a signal generated in the photoelectric converter via a vertical signal line and hold the signal, and a converter configured to perform an analog/digital conversion is provided. In the sample/hold unit, a first sample/hold circuit that samples a signal for when the photoelectric converter is reset and a second sample/hold circuit that samples a signal for when a photoelectric conversion operation is performed are connected to one vertical signal line. The pixel portion is arranged on a first substrate, a part of a group configured by the sample/hold unit and the converter is arranged on a second substrate, and another part of the group is arranged on a third substrate.