Disclosed herein are provided an arrangement of devices suitable to downsize a synchrotron, a synchrotron using such an arrangement, and a particle therapy system using the synchrotron. In the synchrotron, a plurality of deflection magnets and a single defocusing quadrupole magnet are arranged between a first extraction deflector and a second extraction deflector. The defocusing quadrupole magnet is arranged between deflection magnets among the plurality of deflection magnets, a focusing quadrupole magnet is arranged on the side of an inlet of the first extraction deflector, and a focusing quadrupole magnet is arranged on the side of an outlet of the second extraction deflector.