A particle beam therapy system which can surely prevent a beam from being erroneously transported to a treatment room that is not an irradiation target, and can improve safety. The particle beam therapy system comprises a charged particle beam generator for emitting a charged particle beam, a plurality of treatment rooms provided with respective irradiation units, one first beam transport system for transporting the emitted beam toward the downstream side in the direction of beam advance, a plurality of second beam transport systems branched from the first beam transport system and transporting the beam to the corresponding irradiation units in the treatment rooms, a plurality of switching electromagnets for bending the beam transported through the first beam transport system to be introduced to the corresponding second beam transport systems, and a first group of shutters provided downstream of the switching electromagnets and shutting off respective beam paths.