A particle beam therapy system that is capable of irradiating a target area with an irradiation beam suitable for a particle beam therapy using a spot scanning method includes a synchrotron, a beam transport system and an irradiation device. The beam transport system is provided with a beam interrupting device adapted to block supply of a charged particle beam to the irradiation device. The beam interrupting device has a beam shielding magnet, an exciting power supply for the beam shielding magnet and a beam dump. The beam transport system has a bending magnet. The beam shielding magnet is provided on an inlet side of the bending magnet. The beam dump is provided on an outlet side of the bending magnet. A controller controls the exciting power supply to control the timing of an operation of the beam shielding magnet.
