A photodetecting device comprising: a semiconductor substrate including a first principal surface and a second principal surface that oppose each other, and including a plurality of avalanche photodiodes (APD, APD1, APD2) arranged to operate in Geiger mode; and a plurality of through-electrodes electrically connected to corresponding avalanche photodiodes (APD, APD1, APD2) of the plurality of avalanche photodiodes (APD, APD1, APD2) and penetrating through the semiconductor substrate in a thickness direction, wherein the semiconductor substrate includes: a first area (α) in which the plurality of avalanche photodiodes (APD, APD1, APD2) are distributed in at least a first direction; and a second area (β) in which the plurality of through-electrodes are distributed two-dimensionally, characterised in that: the second area (β) is separate to the first area (α) and the first area (α) and the second area (β) are distributed in a second direction orthogonal to the first direction when viewed from a direction orthogonal to the first principal surface (INa), and each of the plurality of through-electrodes distributed two-dimensionally in the second area (β) is electrically connected to a corresponding one of the plurality of the avalanche photodiodes (APD, APD1, APD2) distributed in the first area (α). a semiconductor substrate including a first principal surface and a second principal surface that oppose each other, and including a plurality of avalanche photodiodes (APD, APD1, APD2) arranged to operate in Geiger mode; and a plurality of through-electrodes electrically connected to corresponding avalanche photodiodes (APD, APD1, APD2) of the plurality of avalanche photodiodes (APD, APD1, APD2) and penetrating through the semiconductor substrate in a thickness direction, wherein the semiconductor substrate includes: a first area (α) in which the plurality of avalanche photodiodes (APD, APD1, APD2) are distributed in at least a first direction; and a second area (β) in which the plurality of through-electrodes are distributed two-dimensionally, a first area (α) in which the plurality of avalanche photodiodes (APD, APD1, APD2) are distributed in at least a first direction; and a second area (β) in which the plurality of through-electrodes are distributed two-dimensionally, characterised in that: the second area (β) is separate to the first area (α) and the first area (α) and the second area (β) are distributed in a second direction orthogonal to the first direction when viewed from a direction orthogonal to the first principal surface (INa), and each of the plurality of through-electrodes distributed two-dimensionally in the second area (β) is electrically connected to a corresponding one of the plurality of the avalanche photodiodes (APD, APD1, APD2) distributed in the first area (α). the second area (β) is separate to the first area (α) and the first area (α) and the second area (β) are distributed in a second direction orthogonal to the first direction when viewed from a direction orthogonal to the first principal surface (INa), and each of the plurality of through-electrodes distributed two-dimensionally in the second area (β) is electrically connected to a corresponding one of the plurality of the avalanche photodiodes (APD, APD1, APD2) distributed in the first area (α).