Abstract: An X-ray CT apparatus is capable of obtaining an image of arbitrary size for an arbitrary part of an object to be examined. The X-ray CT apparatus prepares two-dimensional data and three-dimensional data from a plurality of X-ray information obtained by driving an X-ray tube and an X-ray information detector through one rotation around a patient in a range between a lower jaw and the eyes of the patient, and it displays a tomographic image based thereon on a display unit. A rotational mechanism is fitted to a support, a U-shaped arm is mounted on the support with the X-ray tube and the X-ray information inputting means facing each other and fitted, and the image of an arbitrary size of an arbitrary part of the patient is collected and displayed as the patient is supported in a chair which is capable of being electrically-driven in the vertical direction.