Photoelectric conversion device and imaging system

A photoelectric conversion device includes a plurality of pixels arranged to form a plurality of columns, each of the pixels including a photoelectric conversion unit including first and second electrodes, a photoelectric conversion layer between the first and second electrodes, and an insulating layer between the photoelectric conversion layer and the second electrode, an amplifier unit connected to the second electrode and configured to output a signal, and a reset unit for supplying a reset voltage to the second electrode. In accordance with a voltage applied between the first and second electrodes, an accumulating operation for accumulating signal charges and a removing operation for removing the signal charges are alternately executed, the reset unit supplies the reset voltage for at least a part of a horizontal scanning period, and the period during which the reset unit supplies the reset voltage is longer than the horizontal scanning period.