An object of the invention is to provide a medical device which can perform treatment and diagnosis without causing a sense of unease to the patient. The invention includes a substantially ring-shaped support frame provided in such a manner that a central axis through which an isocenter passes is disposed substantially horizontally a substantially ring-shaped moving gantry which slides relative to the support frame and which has an opening at the isocenter side thereof a radiation emitter configured to emit a beam towards the isocenter and a protective cover which covers the radiation emitter and an inner circumferential side of the moving gantry and which moves together with the moving gantry.
