A photodetecting device comprising: at least one semiconductor photodetecting element including a semiconductor substrate in which a photodiode array including a plurality of pixels is formed, the semiconductor substrate having a first principal surface and a second principal surface opposing each other; and a mount substrate disposed to oppose the semiconductor photodetecting element, and having a third principal surface opposing the second principal surface of the at least one semiconductor substrate and a fourth principal surface opposing the third principal surface, the at least one semiconductor photodetecting element being molded with resin; wherein, for each of the at least one semiconductor photodetecting elements, the semiconductor substrate includes a first region in which the plurality of pixels are disposed and a second region located inside the first region to be surrounded by the first region when viewed from a direction in which the first principal surface and the second principal surface oppose each other, a through-hole penetrating through the semiconductor substrate is formed in the second region of the semiconductor substrate and the through-hole is filled with resin, a first electrode disposed on the first principal surface of the semiconductor substrate and electrically connected to the plurality of pixels and a second electrode disposed on the third principal surface of the mount substrate are connected to each other via a first wire inserted through the through-hole, and a third electrode disposed on the second principal surface of the semiconductor substrate and electrically connected to the semiconductor substrate and a fourth electrode disposed on the third principal surface of the mount substrate are in surface contact with an electrically conductive resin interposed between said third and fourth electrodes to thermally connect the second principal surface and the third principal surface, wherein the third and fourth electrodes are disposed at positions corresponding to each other. at least one semiconductor photodetecting element including a semiconductor substrate in which a photodiode array including a plurality of pixels is formed, the semiconductor substrate having a first principal surface and a second principal surface opposing each other; and a mount substrate disposed to oppose the semiconductor photodetecting element, and having a third principal surface opposing the second principal surface of the at least one semiconductor substrate and a fourth principal surface opposing the third principal surface, the at least one semiconductor photodetecting element being molded with resin; wherein, for each of the at least one semiconductor photodetecting elements, the semiconductor substrate includes a first region in which the plurality of pixels are disposed and a second region located inside the first region to be surrounded by the first region when viewed from a direction in which the first principal surface and the second principal surface oppose each other, a through-hole penetrating through the semiconductor substrate is formed in the second region of the semiconductor substrate and the through-hole is filled with resin, a first electrode disposed on the first principal surface of the semiconductor substrate and electrically connected to the plurality of pixels and a second electrode disposed on the third principal surface of the mount substrate are connected to each other via a first wire inserted through the through-hole, and a third electrode disposed on the second principal surface of the semiconductor substrate and electrically connected to the semiconductor substrate and a fourth electrode disposed on the third principal surface of the mount substrate are in surface contact with an electrically conductive resin interposed between said third and fourth electrodes to thermally connect the second principal surface and the third principal surface, wherein the third and fourth electrodes are disposed at positions corresponding to each other.