An X-ray apparatus includes a two-dimensional pixel array having rectangular pixels outputting an electrical signal responsively to an incident X-ray photon. This array has a row direction oblique to a scan direction. When viewing in the scan direction, a pixel group is provided solely or repeatedly, the pixel group being composed of “M rows × N pieces” of pixels (M is a positive integer equal to or larger than 1, N is a positive integer equal to or larger than 2, and M and N have a relationship of prime numbers). The pixel group occupies a quadrangle whose diagonal line is parallel with the scan direction. In a memory space, the frame data from the pixels are converted to frame data in a Cartesian coordinate system having a row direction which is in parallel with the scan direction and a column direction orthogonal to the row direction.