An X-ray computer tomography apparatus includes a cone beam X-ray tube X-rays, a two-dimensional array type X-ray detector, a rotating mechanism which supports the X-ray tube, together with the X-ray detector, so as to be rotatable around the object, a reconstruction processing unit which reconstructs a full scan image based on projection data, of the projection data, which corresponds to a view count corresponding to one rotation and also reconstructs a short scan image based on projection data corresponding to a view count smaller than the view count corresponding to one rotation, a CT value shift distribution generating unit which generates a spatial distribution of CT value shifts originating from the smaller view count based on the full scan image and the short scan image, and a correcting unit which corrects the short scan image based on the spatial distribution of the CT value shifts.