Provided is an X-ray CT device whereby a high resolution can be efficiently obtained in taking an image and X-ray detecting elements in a small detector size can be fully utilized. The X-ray CT device according to one embodiment of the present invention comprises an X-ray tube, an X-ray detector and a controlling means. The X-ray detector comprises at least two divided scopes. One scope comprises a small detection scope wherein small-sized X-ray detecting elements for detecting X-rays radiated from the X-ray tube are arranged. The other scope comprises a large detection scope wherein large-sized X-ray detecting elements for detecting X-rays radiated from the X-ray tube are arranged. The controlling means is configured so as to select the small detection scope or the large detection scope.