A photoelectric conversion device comprises: a plurality of photoelectric conversion elements each having a photo-sensing surface; insulation films; a plurality of light-guiding portions arranged above the insulation films, each of the plurality of light-guiding portions guiding light on the photo-sensing surface of each of the plurality of photoelectric conversion elements; and boundary portions, each of the boundary portions defines a boundary between the adjacent light-guiding portions and is formed of a material lower in refractive index than a material that forms the plurality of light-guiding portions, wherein a width of each of the boundary portions is not more than half a shortest wavelength in a wavelength range of visible light, and a height from a lower surface to an upper surface of each of the plurality of light-guiding portions is not less than double a longest wavelength in the wavelength range of visible light.