An X-ray CT apparatus, wherein a drum type rotation frame is rotatably supported by a fixed circular frame so as to surround an outer surface of the drum type rotation frame through a plurality of bearings provided between an inner surface of the fixing circular frame and an outer surface of the drum type rotation frame, for example in ring-like configuration. When the drum type rotation frame receives a large centrifugal acceleration due to a high speed rotation, outside expansion of the drum type rotation frame can be constrained due to both the rigidity of the fixed frame and the rigidity of the plurality of bearings provided on the outer surface of the rotation frame, thereby to maintain the relative positions of the X-ray tube and the X-ray detector and prevent deterioration of reconstructed images.