To provide a X-ray CT apparatus capable of correcting displacement of the focus of the X-ray in good response even if occurring in the body axis direction of a test subject.

A X-ray CT apparatus includes a rotor body 4 rotating around a subject 2, a X-ray tube device comprising a X-ray tube 5b which irradiates X-ray toward the subject 2 mounted on the rotor body 4, and a X-ray detector 6 having the subject 2 inside which is mounted on the rotor body 4 opposite to the X-ray tube 5 and detects X-ray transmitted in the subject 2, and consists of: a deflecting electromagnet 9 which is mounted near the outer circumference of an outer peripheral device storing the X-ray tube of the above X-ray tube device and forms a deflecting magnetic field B for deflecting an electronic beam 5c released from a negative electrode 5a in the X-ray tube 5; a focus displacement detector 10 for detecting the focus displacement toward the body axis direction of the X-ray tube 5; and a deflecting control means 11 which adjusts an exciting current of the above deflecting electromagnet 9 in order that the focus displacement is zero toward the body axis direction detected by the focus displacement detector 10.