A charged particle beam irradiation system includes: an accelerator which accelerates charged particles along an orbit, thereby emitting a charged particle beam a gantry on which the accelerator is mounted and which can rotate or oscillate around a given axis and an irradiation section which is mounted on the gantry and can irradiate the charged particle beam emitted from the accelerator, toward an irradiated body, wherein a shielding body which is provided in the gantry and shields radiation that is radiated from a side of the accelerator, which may be a face intersecting the radial direction of the orbit, is disposed.
