To provide an X-ray CT apparatus preventing the deterioration of the image quality even if rotating a rotary frame attached with an X-ray tube and an X-ray detector at a high speed. This X-ray CT apparatus disposed with the X-ray tube and the X-ray detector opposed to each other and having a cylindrical rotary frame rotating around a subject, rotatably supports the cylindrical rotary frame to a fixed frame surrounding an outer circumference of its annular part, and interposes a bearing member between the internal circumferential face side of the fixed frame and the outer circumferential face side of the annular part of the cylindrical rotary frame so that, even if the cylindrical rotary frame is going to outward expand by receiving a large centrifugal acceleration when rotating the cylindrical rotary frame at a high speed, rigidity between the fixed frame and the bearing member provided between the fixed frame and the rotary frame prevents it to prevent the displacement of the relative position between the X-ray tube and the X-ray detector and prevent the deterioration of the image quality caused by the position displacement.