CHARGED PARTICLE BEAM IRRADIATION SYSTEM

Provided is a charged particle beam irradiation system (1) capable of appropriately irradiating an irradiation target with a charged particle beam (B) . By a snout degrader (30) adjusting the penumbra (P) of a charged particle beam (B), it is possible to suppress the outside of a tumor (14) being irradiated with the charged particle beam (B) when an irradiator (2) irradiates the vicinity of the boundary portion of the tumor (14). Here, the irradiator (2) is provided with a holder (60) holding the snout degrader (30). Accordingly, alignment can be easily performed between the charged particle beam (B) with which the tumor (14) is irradiated and the snout degrader (30) . Accordingly, the irradiator (2) is capable of irradiating the tumor (14) with the charged particle beam (B) in a state where the penumbra (P) is adjusted at an appropriate position by the snout degrader (30). In the present embodiment, the snout degrader 30 has only to be held by the holder (60), and thus the alignment is performed with ease.