1. An X-ray CT apparatus comprising: a scanning table for placing a subject thereon and moving the subject placed thereon; a scanning gantry comprising an X-ray generator, an X-ray detector for detecting the X rays in opposition to the X-ray generator, and a rotation device for rotating the X-ray generator and the X-ray detector, for causing the X-ray generator to expose X rays to the subject moved by the scanning table while the X-ray generator and the X-ray detector are being rotated about the subject, and performing a scan for causing the X-ray detector to detect the X rays transmitted through the subject thereby to acquire X-ray projection data; image reconstructing device for image-reconstructing the X-ray projection data acquired by the scanning gantry; image display device for displaying a tomographic image reconstructed by the image reconstructing device; and imaging condition setting device for setting an imaging condition including a parameter for operating the scanning gantry and/or a parameter for causing the scanning table to move the subject upon execution of the scan, wherein the image reconstructing device reconstructs the X-ray projection data using the parameter for operating the scanning gantry and/or the parameter for causing the scanning table to move the subject set by the imaging condition setting device as the imaging condition.