Accelerator and particle therapy system

An accelerator, having a pair of cores formed in disk shape, a pair of magnetic poles fixed to circular surfaces of the cores, a pair of coils placed around the magnetic poles,

• having a space between the pair of the magnetic poles for circulating and accelerating ion beams,
• wherein the pair of the magnetic poles has a plurality of depression and projection structures arranged along orbits of the ion beams circulating, and the magnetic poles are plane-symmetric with respect to an orbit plane created by the orbits of the ion beams circulating as well as plane-symmetric with respect to one of vertical planes perpendicular to the orbit plane,
• the pair of the magnetic poles has a depression structure of the plurality of depression and projection structures, in a position intersecting with the vertical plane, and a boundary surface between the depression structure placed in the position intersecting with the vertical plane and a projection structure adjacent to the depression structure has unanimously either a projection shape or a depression shape with respect to the vertical plane.