A first photoelectric conversion element, which detects light and converts the light into photoelectrons has: one first MOS diode having a first electrode formed on a semiconductor base body with an insulator therebetween; and a plurality of second MOS diodes, each of which has a second electrode formed on the semiconductor base body with the insulator therebetween. The first electrode of the first MOS diode has, when viewed from the upper surface, a comb-like shape wherein a plurality of branch portions are branched from one electrode portion. Each second electrode of each of the second MOS diodes is, when viewed from the upper surface, separated from the first electrode, and is disposed to nest between the branch portions of the first electrode.