On a wiring board 21, first and second semiconductor detection device arrays 22a and 22b are arranged along a depth direction (Y-axial direction). Each of the first and the second semiconductor detection device arrays 22a and 22b is composed by arranging six semiconductor detection devices 231 through 236 in one line in an arrangement direction (X-axial direction). Guard members 28a and 28b are arranged one on each end in the arrangement direction. In the semiconductor detection devices 231 through 236 of the first and the second semiconductor detection device arrays 22a and 22b, a kth (k is one of the number from 1 to 6) semiconductor detection device 23k from a reference line Xa is arranged by being shifted from others by ½ of a gap PT of the semiconductor detecting devices 231 through 236 in the arrangement direction.
