To provide a photoelectric conversion device having a high S/N ratio at a low cost. The photoelectric conversion device includes a light-receiving element that includes: a first semiconductor region of a first conductivity type; a second semiconductor region of a second conductivity type formed in the first semiconductor region; and a gate electrode formed close to the second semiconductor region through an insulator. In the photoelectric conversion device, a surface state of the first semiconductor region below the gate electrode can be controlled between two states consisting of an inversion state and an: accumulation state.