An X-ray CT apparatus includes an X-ray tube, an X-ray detector, and a control unit. The X-ray detector includes at least two divided ranges. One range includes a small detection range in which X-ray detection elements of a small size for detecting the X-rays radiated from the X-ray tube are arrayed. The other range includes a large detection range in which the X-ray detection elements of a large size for detecting the X-rays radiated from the X-ray tube are arrayed. The control unit is configured to select the small detection range or the large detection range. The X-ray CT apparatus can efficiently achieve high resolution upon imaging and, further, is capable of fully utilizing X-ray detection elements of a small detector size.
