Photoelectric conversion device and imaging system

A photoelectric conversion device includes: a first semiconductor region of a first conductivity type, which configures a first photoelectric conversion element; a second semiconductor region of the first conductivity type, which configures a second photoelectric conversion element; a third semiconductor region of the first conductivity type; a fourth semiconductor region of the first conductivity type; a first gate electrode, configuring a first transfer transistor conjointly; and a second gate electrode, configuring a second transfer transistor. At a side of the first gate electrode which is toward the first semiconductor region in plan view of the surface of the semiconductor substrate, a length of the side of the first gate electrode toward the first semiconductor region, is shorter than a length of the active region, and a length of the side of the first gate electrode toward the first semiconductor region, is longer than a length of the first semiconductor region.