A photoelectric conversion device includes a photoelectric converter, a transistor having a gate to which a voltage corresponding to charges generated by the photoelectric converter is supplied, a control line connected to a first main electrode of the transistor, and a readout unit configured to read out a signal corresponding to a voltage of the gate, and a voltage controller configured to change a voltage of the control line. The readout unit generates a digital signal corresponding to the voltage of the gate, based on a current flowing through a second main electrode of the transistor during a period in which the voltage controller changes the voltage of the control line.