In a photoelectric conversion device capable of adding signals of photoelectric conversion elements included in each of photoelectric conversion units, each of the photoelectric conversion elements includes a first semiconductor region of a first conductivity type for collecting a signal charge, a second semiconductor region of a second conductivity type is arranged between the photoelectric conversion elements arranged adjacent to each other and included in the photoelectric conversion unit, and a third semiconductor region of the second conductivity type is arranged between the photoelectric conversion elements arranged adjacent to each other among the plurality of photoelectric conversion elements and included in different photoelectric conversion units arranged adjacent to each other. An impurity concentration of the second semiconductor region is lower than an impurity concentration of the third semiconductor region.