An X-ray computerized tomographic apparatus includes an X-ray tube device configured to irradiate an object to be examined with a pyramidal X-ray beam, a detector which has a plurality of detecting elements arrayed in a slice direction in which X-rays transmitted through the object are detected, a data extending unit which creates virtual data corresponding to an extension region located outside a region in which the detecting elements are arranged in the slice direction on the basis of real data detected by the detecting element, and a reconstructing unit which reconstructs image data on the basis of the real data and virtual data.
