An X-ray computed tomographic apparatus comprises a scanner to scan in a three-dimensional region of a subject by X-rays, a storing unit to store projection data acquired by the scanning, a reconstruction processing unit to generate volume data which corresponds to a three-dimensional region, based on the stored projection data, an MPR processing unit to generate slice image data relating to three-direction slice planes from the volume data, a displaying unit to display the slice image data together with a graphic element representing a reconstruction range, an operating unit to operate the graphic element, and a reconstruction processing unit to reconstruct tomographic image data which corresponds to the reconstruction range represented by the graphic element, based on the stored projection data.