Plural detection boards are stacked and fixed. The detection board has a wiring board, a semiconductor detection device fixed on an upper surface of the wiring board and configured to detect radiation, and a spacer fixed on the upper surface of the wiring board. Each of the detection boards is provided so that the semiconductor detection device and the spacer have a designated positional relationship. In addition, the spacers are stacked and matched in an X-Y plane surface with each other so that the detection boards are fixed by fixing members.