Techniques are provided that enable displaying of medical images that depict cyclic motions in the subject. An X-ray CT system scans, with X-rays, the subject whose targeted region is experiencing a cyclic motion and acquires detection data. This X-ray CT system comprises a reconstruction processor, a moving image creator, and a display controller. The reconstruction processor generates a plurality of sets of volumetric data based on a plurality of sets of detection data that have been acquired during one cycle of the cyclic motion. The moving-image creator creates a moving image that shows the cyclic motion, on the basis of at least a part of the plural sets of volumetric data. The display controller superposes the moving image over an image based on the volumetric data and displays these images on the display unit.