An X-ray computed tomographic apparatus of the invention includes a display portion to display, on a screen, a scanogram related to a subject together with a quadrilateral frame line specifying a reconstruction range, an input portion to input a command to transform the frame line specifying the reconstruction range to a parallelogram or rotate the frame line specifying the reconstruction range, a gantry to perform scanning in a scan range corresponding to the reconstruction range, and a reconstruction portion to reconstruct image data related to plural slices, parallel to one another and included in the reconstruction range, slice-by-slice on the basis of projection data acquired by the scanning.