PROBLEM TO BE SOLVED: To improve efficiency of an image reconstruction processing and enlarge a utilization range of projection data in an X-ray computer tomographic apparatus capable of performing helical scan.SOLUTION: An X-ray computer tomographic apparatus includes: an X-ray tube an X-ray detector a rotation mechanism supporting the X-ray tube so as to be rotatable around the periphery of a subject control means for controlling the rotation mechanism setting means for setting a fluoroscopic direction of a scanogram and generation means for generating a first scanogram corresponding to a first fluoroscopic direction set by the setting means on the basis of the obtained projection data, and a second scanogram corresponding to the first fluoroscopic direction and having spatial resolving power higher than that of the first scanogram on the basis of the enlargement instruction to the first scanogram.
