PROBLEM TO BE SOLVED: To provide a particle beam accelerator and a particle beam therapy device in which beam extraction efficiency is enhanced more than before.SOLUTION: A particle beam accelerator has disc-like upper return yoke 4, a lower return yoke 5 and a pair of upper magnetic pole 8 and a lower magnetic pole 9 fixed to the disc-like surfaces of the upper return yoke 4 and the lower return yoke 5. A space for circulating an ion beam between the upper and lower magnetic poles 8, 9 and accelerating is formed therebetween. The upper and lower magnetic poles 8, 9 have multiple recesses 21-24 and protrusions 31-34 along the circulation orbit of ion beam, and include a magnet device 1 that is plane symmetric with a horizontal symmetry plane 2 formed by the circulation orbit of the ion beam, and plane symmetric with one perpendicular surface perpendicular to the horizontal symmetry plane 2, where the magnetic pole intervals 101-103 between the recesses 21-24 of the upper and lower magnetic poles 8, 9 may be different.SELECTED DRAWING: Figure 5COPYRIGHT: (C)2019,JPO&INPIT【課題】ビーム取り出し効率を従来より高めた粒子線加速器、粒子線治療装置を提供する。【解決手段】円盤状の上リターンヨーク４，下リターンヨーク５および上リターンヨーク４，下リターンヨーク５の円盤状の面に固定された一対の上部磁極８，下部磁極９を有しており、上部磁極８，下部磁極９の間にイオンビームを周回させ加速させる空間が形成され、上部磁極８，下部磁極９が、イオンビームの周回する軌道に沿って複数の凹部２１～２４および凸部３１～３４を有するとともに、イオンビームの周回する軌道が形成する水平対称面２に対して面対称、かつ水平対称面２に垂直な垂直面の一つに面対称になっている磁石装置１を備え、上部磁極８，下部磁極９の凹部２１～２４の間の磁極間隔１０１～１０３が異なるものがある。【選択図】 図５
