A photodetecting device comprising: a semiconductor substrate (50A; 50B) including a first principal surface and a second principal surface that oppose each other; a plurality of avalanche photodiodes each including a light receiving region disposed at the first principal surface side of the semiconductor substrate (50A; 50B), the avalanche photodiodes being arranged two-dimensionally at the semiconductor substrate (50A; 50B), and operating in Geiger mode; and a through-electrode electrically connected to a corresponding light receiving region, wherein the through-electrode is provided in a through-hole penetrating through the semiconductor substrate (50A; 50B) in a thickness direction in an area where the plurality of avalanche photodiodes are arranged two-dimensionally, characterized in that: at the first principal surface of the semiconductor substrate (50A; 50B), a groove (13; 23) surrounding the through-hole is formed in an area between the through-hole and the light receiving region adjacent to the through-hole, and a first distance (β) between a first edge of the groove (13; 23) and an edge of the through-hole surrounded by the groove (13; 23) is longer than a second distance (α) between a second edge of the groove (13; 23) and an edge of the light receiving region adjacent to the through-hole surrounded by the groove (13; 23); wherein the first edge of the groove is proximal to the through-hole and the second edge of the groove is distal to the through-hole; and wherein the first distance (β) is the shortest distance between the first edge of the groove (13; 23) and the edge of the through-hole surrounded by the groove (13; 23) and the second distance (α) is the shortest distance (α) between the second edge of the groove (13; 23) and the edge of the light receiving region adjacent to the through-hole surrounded by the groove (13; 23). a semiconductor substrate (50A; 50B) including a first principal surface and a second principal surface that oppose each other; a plurality of avalanche photodiodes each including a light receiving region disposed at the first principal surface side of the semiconductor substrate (50A; 50B), the avalanche photodiodes being arranged two-dimensionally at the semiconductor substrate (50A; 50B), and operating in Geiger mode; and a through-electrode electrically connected to a corresponding light receiving region, wherein the through-electrode is provided in a through-hole penetrating through the semiconductor substrate (50A; 50B) in a thickness direction in an area where the plurality of avalanche photodiodes are arranged two-dimensionally, characterized in that: at the first principal surface of the semiconductor substrate (50A; 50B), a groove (13; 23) surrounding the through-hole is formed in an area between the through-hole and the light receiving region adjacent to the through-hole, and a first distance (β) between a first edge of the groove (13; 23) and an edge of the through-hole surrounded by the groove (13; 23) is longer than a second distance (α) between a second edge of the groove (13; 23) and an edge of the light receiving region adjacent to the through-hole surrounded by the groove (13; 23); wherein the first edge of the groove is proximal to the through-hole and the second edge of the groove is distal to the through-hole; and wherein the first distance (β) is the shortest distance between the first edge of the groove (13; 23) and the edge of the through-hole surrounded by the groove (13; 23) and the second distance (α) is the shortest distance (α) between the second edge of the groove (13; 23) and the edge of the light receiving region adjacent to the through-hole surrounded by the groove (13; 23). at the first principal surface of the semiconductor substrate (50A; 50B), a groove (13; 23) surrounding the through-hole is formed in an area between the through-hole and the light receiving region adjacent to the through-hole, and a first distance (β) between a first edge of the groove (13; 23) and an edge of the through-hole surrounded by the groove (13; 23) is longer than a second distance (α) between a second edge of the groove (13; 23) and an edge of the light receiving region adjacent to the through-hole surrounded by the groove (13; 23);