PURPOSE: To provide an X-ray CT device which can be positioned simply without moving a bed or plate many times to guide a subject position of a testee to a photographing position.

CONSTITUTION: In an X-ray CT device provided with a means 3 to radiate an X-ray to a testee P for X-ray photography, an X-ray detector 4 to detect the X-ray coming through the testee P, a bed 2 for the testee P to be placed to guide the testee P to a photographing position in an aperture part 14 of a frame 1, and projectors 15a-15c to position a subject position of the testee P placed on the bed in front of the aperture part 14 of the frame 1, the projectors 15a-15c are set movable, and a light marker M from the projector 15 is set to be movable in a desired angular direction to position the subject position of the testee P. The bed 2 is then drive-controlled based on displacement quantity of the light marker M at this time, thereby the subject position of the testee P is guide to the photographing position automatically.