An X-ray CT apparatus that achieves a higher quality of reconstructed CT images by preventing displacements of relative positions of the X-ray tube and the X-ray detector from occurring, including a front side rotation frame configured to mount at least one X-ray tube and at least one X-ray detector facing the X-ray tube, and a rear side rotation frame configured to mount rotation units other than the X-ray tube and the X-ray detector in order to access both sides of the gantry.