1. An X-ray CT system comprising: an X-ray data collection device for enabling an X-ray generator and an X-ray area detector, which is opposed to the X-ray generator in order to detect X-rays and structured with detector elements arranged in the form of a matrix, to rotate about a center of rotation located between them, and collect projection data items produced from X-rays transmitted by a subject lying on a subject support unit between the X-ray generator and the X-ray area detector; an image reconstruction device for reconstructing a plurality of tomographic images corresponding to each position in a body axis direction of the subject by using the projection data items collected by the X-ray data collection device; and an image display device for displaying the plurality of reconstructed tomographic images; wherein at least one of the image reconstruction device and the image display device is configured to: detect a reference point in each of the plurality of reconstructed tomographic images; measure a deviation of each of the plurality of reconstructed tomographic images in a y direction that is a height direction of the subject support unit, or a deviation thereof in an x direction that is a width direction of the subject support unit and the y direction by identifying a position of a reference point in each of the plurality of reconstructed tomographic images and specifying a difference between each reference point position, wherein each reference point is located at an outer edge of the subject support unit; compensate for the deviations so as to minimize a difference between each reference point position; and produce at least one of a three-dimensional display image, a multiplanar reformation display image, and a maximum-intensity projection display image using the compensated plurality of reconstructed tomographic images.