PROBLEM TO BE SOLVED: To provide an X-ray CT capable of irradiating a subject with X-rays at a proper position of a back surface of the subject even during high-speed rotation.SOLUTION: An X-ray CT apparatus of an embodiment includes an imaging means for performing imaging while rotating an X-ray tube and an X-ray detector arranged facing each other holding a subject on a bed therebetween around the body axis of the subject, and a control means for controlling the imaging means, and irradiates the subject with X-rays when the X-ray tube is rotated to the back surface side of the subject. The X-ray CT apparatus further includes a position detection means, an X-ray CT determination means, and an irradiation instruction means. The position detection means outputs a detection signal when the X-ray tube is rotated to a predetermined position. A comparator compares the detection signal with a predetermined reference signal, and outputs a comparison result indicating whether or not the detection signal has been outp
