A circular accelerator capable of generating plasma in an internal ion source with a configuration that can be easily maintained, and a particle beam irradiation apparatus including the same. The accelerator includes a pair of opposed main magnetic poles 1 that generate a magnetic field that circulates the ion beam, a high-frequency acceleration electrode 7 that accelerates the ion beam, and an internal structure that is disposed in the main magnetic pole 1. A discharge vessel 5 and an external particle source 3 disposed outside the main magnetic pole 1 are used, and plasma is generated in the internal discharge vessel 5 by particles incident from the external particle source 3 to the internal discharge vessel 5. Extract ion beam from [Selection] Figure 4【課題】メンテナンスが容易な構成で、内部イオン源内にプラズマを生成することが可能な円形加速器とそれを備えた粒子線照射装置を提供する。【解決手段】加速器は、イオンビームを周回させる磁場を発生させる、対向して配置された一対の主磁極１と、イオンビームを加速する高周波加速電極７と、主磁極１内に配置された内部放電容器５と、主磁極１外に配置された外部粒子源３と、を有し、外部粒子源３から内部放電容器５へ入射させた粒子で内部放電容器５内にプラズマを生成し、プラズマからイオンビームを引き出す。【選択図】図４
