An optical detection unit comprising: a first wiring substrate that has a first main surface; a plurality of optical detection chips that each have a light receiving surface (S1s) and a rear surface (S1r) on a side opposite to the light receiving surface (S1s) 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; characterized by: a light transmitting portion that is provided on the light receiving surface (S1s); and a light shielding portion that has light reflection properties or light absorption properties, wherein each of the plurality of optical detection chips 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 (S1r) faces the first main surface, wherein the light shielding portion is provided at least on the light transmitting portion side of the light receiving surface (S1s) in an intermediate region positioned between the optical detection chips adjacent to each other when seen in a first direction intersecting the first main surface and wherein the light shielding portion is provided in a region formed between the light transmitting portions which are arranged on the light receiving surfaces (S1s) of the optical detection chips adjacent to each other, wherein the light transmitting portion includes a light incidence surface (S2s) on a side opposite to a surface on the light receiving surface (S1s) side, and wherein an end portion (Fa) of the light shielding portion on the light incidence surface (S2s) side is positioned on the first main surface side of the light incidence surface (S2s) in the first direction and is recessed toward the first main surface side. a first wiring substrate that has a first main surface; a plurality of optical detection chips that each have a light receiving surface (S1s) and a rear surface (S1r) on a side opposite to the light receiving surface (S1s) 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 (S1s); and a light shielding portion that has light reflection properties or light absorption properties, wherein each of the plurality of optical detection chips 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 (S1r) faces the first main surface, wherein the light shielding portion is provided at least on the light transmitting portion side of the light receiving surface (S1s) in an intermediate region positioned between the optical detection chips adjacent to each other when seen in a first direction intersecting the first main surface and wherein the light shielding portion is provided in a region formed between the light transmitting portions which are arranged on the light receiving surfaces (S1s) of the optical detection chips adjacent to each other, wherein the light transmitting portion includes a light incidence surface (S2s) on a side opposite to a surface on the light receiving surface (S1s) side, and wherein an end portion (Fa) of the light shielding portion on the light incidence surface (S2s) side is positioned on the first main surface side of the light incidence surface (S2s) in the first direction and is recessed toward the first main surface side.