An optical detection unit includes a first wiring substrate that has a first main surface, a plurality of optical detection chips that each have a light receiving surface and a rear surface on a side opposite to the light receiving surface and are two-dimensionally arranged on the first main surface, a first bump electrode that electrically connects the optical detection chip to the first wiring substrate, a light transmitting portion that is provided on the light receiving surface, and a light shielding portion that has light reflection properties or light absorption properties. The optical detection chip includes a Geiger-mode APD and is mounted on the first wiring substrate by the first bump electrode in a state in which the rear surface faces the first main surface.