In a photodetector using GePDs, a photodetector having small change in light sensitivity due to temperature is provided. A photodetector includes a plurality of photodiodes formed on a silicon substrate and having germanium or a germanium compound in a light absorption layer, and two chips of integrated circuits arranged parallel to two sides connected to one corner of the silicon substrate, respectively, the two integrated circuits are connected to photodiodes formed on the silicon substrate, two or more of the photodiodes are arranged equidistantly from the integrated circuit that is parallel to one side connected to the one corner, and the numbers of equidistantly arranged photodiodes are equal, when viewed from the integrated circuits.