An X-ray computed tomographic apparatus includes an X-ray tube which generates X-rays, an X-ray detector which detects X-rays transmitted through a subject and generates projection data, and a reconstruction unit which generates a plurality of original volume data at different scanning times based on the projection data. This apparatus includes an unit which obtains difference volume data corresponding different scanning times by performing difference processing between original volume data at adjacent scanning times, an unit which extracts a blood vessel image on the basis of original volume data before and after the injection of a contrast medium, and an unit which generates a display image by providing the blood vessel image with color or luminance information corresponding to the arrival time of the contrast medium on the basis of the blood vessel image and the plurality of difference volume data corresponding to the different scanning times.
