DETECTOR

There is provided a detector capable of securing space for arranging pixels in the vicinity of edges of adjacent readout chips according to design of counting circuits. A 2-dimensional hybrid pixel array detector configured to detect radioactive rays, including a detection unit configured to detect the radioactive rays incident in a region of each pixel 115, and a plurality of the readout chips including counting circuits 121 respectively connected to each of the pixels 115, the counting circuits 121 having a smaller set pitch than the pixels 115 along a certain direction in a detection surface, the regions occupied by the pixels and counting circuits corresponding to the pixels overlapping at least partially, and the connection being made in the overlapping regions.