This invention discloses a photoelectric conversion device. The photoelectric conversion device includes a pixel array in which a plurality of pixels are arrayed in a row direction and a column direction, a plurality of readout circuits which read out signals from pixels for respective columns in the pixel array, and a control unit which controls the plurality of readout circuits, wherein each of the plurality of readout circuits includes a holding unit which holds a reference voltage supplied from an external power source, an operational amplification unit which amplifies the signals from the pixels for each column based on the reference voltage held in the holding unit, and a disconnection unit which electrically disconnects the external power source and the holding unit, and the control unit controls the disconnection unit to electrically disconnect the external power source and the holding unit when the operational amplification unit amplifies the signals from the pixels for each column.