A photoelectric conversion device according to one embodiment includes a first transistor and a first photoelectric conversion element disposed on a first region, a second transistor disposed on a second region, an insulating layer that covers the first transistor, the first photoelectric conversion element, and the second transistor, and a first terminal that is disposed on the insulating layer, is electrically connected to one of the first transistor and the first photoelectric conversion element, and is connectable to an outside. The second transistor is a dummy transistor of the first transistor.