Light detection device

A light detection device, comprising:

• a light detection board having a main surface and including a plurality of pixels disposed in a direction along the main surface;
• and
• a circuit board that includes a plurality of MOS switch circuits arranged in the direction along the main surface and electrically connected to corresponding pixels among the plurality of pixels, wherein:
• each of the pixels includes a plurality of avalanche photodiodes each forming a light receiving region and is configured to operate in a Geiger mode,
• the plurality of avalanche photodiodes forms a plurality of light receiving regions arranged in the direction along the main surface in a pixel area occupied by a corresponding pixel among the plurality of pixels,
• a MOS switch circuit region occupied by the MOS switch circuits overlaps with the plurality of light receiving regions formed in the pixel area when viewed from a direction perpendicular to the main surface,
• an area of the MOS switch circuit region is larger than an area of one of the light receiving regions formed in the pixel area and less than or equal to an area of the pixel area, when viewed from the direction perpendicular to the main surface, and
• the plurality of avalanche photodiodes included in each of the pixels is electrically connected in parallel to each other and is each connected to one of the MOS switch circuits.