To reduce the exposure of a subject to X rays in diagnosing the subject by using an X-ray CT apparatus.

The X-ray CT apparatus includes: an X-ray tube 8 for emitting X rays; an X-ray detector 9 for detecting the X rays emitted from the X-ray tube 8 and penetrating the subject P; a cradle 1 in which the X-ray tube 8 and the X-ray detector 9 are disposed opposite to each other and which has an opening 27 into which the subject P irradiated with X rays is delivered; a reconstruction processing part for reconstructing a tomographic image based on transmitted X ray data detected by the X-ray detector 9; a position detection sensor 11 disposed in the peripheral edge of an opening 9 for detecting position information of the subject P delivered into the opening 9; and a camera 12 for capturing camera images of the subject P in the range of positions detected by the position detection sensor 11.

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