When the IMRT technology for a radiation therapy system utilizing an X-ray or the like is applied as it is to a particle beam therapy system having a conventional wobbler system, there is posed the problem that it is required to utilize two or more boluses. The objective of the present invention is to solve the problem of excess irradiation in IMRT by a particle beam therapy system. More specifically, the problem of excess irradiation in IMRT by a particle beam therapy system is solved by raising the irradiation flexibility in the depth direction, without utilizing a bolus.There is provided a particle beam irradiation apparatus (58) having a scanning irradiation system (34) that performs scanning with a charged particle beam (1) accelerated by an accelerator and being mounted in a rotating gantry for rotating the irradiation direction of the charged particle beam (1); the particle beam irradiation apparatus (58) comprises a columnar-irradiation-field generation apparatus (4) that generates a columnar irradiation field by enlarging the Bragg peak of the charged particle beam (1).