Patent Number: 
Section: claims

1. A charged particle beam irradiation apparatus that irradiates a particle beam to a subject, comprising:a particle beam generation unit from which the particle beam is radiated;a ridge filter, including a plurality of ridges, exhibiting a cyclic thickness distribution for causing the particle beam to exhibit a desired energy distribution, wherein a bottom of each ridge from the plurality of ridges is arranged at an angle different from respective angles of bottoms of the remaining ridges from the plurality of ridges. 2. The charged particle beam irradiation apparatus according to claim 1, wherein a bottom of each ridge from the plurality of ridges of the ridge filter is arranged to be perpendicular to an entering direction of the particle beam. 3. The charged particle beam irradiation apparatus according to claim 1, wherein a bottom of each ridge from the plurality of ridges of the ridge filter is further arranged at a position different from respective positions of bottoms of the remaining ridges from the plurality of ridges. 4. The charged particle beam irradiation apparatus according to claim 1, wherein the ridge filter has the arrangement spacing for each ridge modulated in a direction, in which a cyclic depth distribution is created, according to a change in the angle of each ridge. 5. The charged particle beam irradiation apparatus according to claim 1, wherein each ridge from the plurality of ridges is a bar ridge, and a shape of a bar ridge is varied depending on a distance from the center of a radiation field in the long-side direction of the ridge filter. 6. The charged particle beam irradiation apparatus according to claim 1, wherein a plurality of ridge filters are prepared in association with different conditions for radiation-field formation, and selectively disposed on a beam path, along which the particle beam passes, according to a desired condition for radiation-field formation.