A method and apparatus for reducing the contrast of a tomographic image due to crosstalk and the occurrence of artifacts and improve the quality of the tomographic image. Detection data are subjected to fitting processing in such a manner that, of the data generated by an X-ray detected by X-ray detection elements disposed in array form in a plurality of X-ray detection modules disposed adjacent to one another, first detection data generated by the X-ray detected by X-ray detection elements adjacent to a boundary between the plurality of X-ray detection modules are adapted to waveform data based on second detection data generated by the X-ray detected by X-ray detection elements lying around the adjacent X-ray detection elements.