Provided is a medical X-ray CT imaging apparatus including: a base (22); a support part (30) including a support arm part (30) that supports an X-ray source (36) and an X-ray detector (37) so as to be opposed to each other, and a rotation support part that supports the support arm part (32) in a rotatable manner with respect to the base (22); and a rotary drive part that rotatively drives the support part (30). At least one of the base (22) and the rotary support part (40) includes a cavity (48) forming a space around a rotation axis (A). The cavity (48) is provided with a cylindrical body (60) disposed in a rotatable state with respect to the support part (30).