Disclosed herein is a particle beam therapy system which includes a synchrotron which accelerates beams of charged particles to a desired energy level and permits extraction of the beams of charged particles exceeding the stability limit, an irradiation device which irradiates an object with the beams of charged particles, a beam transport system which conducts the beams of charged particles extracted from the synchrotron to the irradiation device, and a control unit which works in such a way as to remove part of the beams of charged particles circling in the synchrotron and allow the rest of the circling beams of charged particles to be extracted from the synchrotron and conducted to the irradiation device. The particle beam therapy system produces irradiation beams suitable for high-precision particle beam therapy by the spot scanning method or the like.
