An object of the present invention is to provide a particle beam treatment system that can realize the reduction of treatment time for a specific patient, compared with treatment time in a conventional type. A control unit of a control system 3 controls a beam routing system 2 and irradiation devices 40A-40D so as to maintain the occupation of an accelerator 1 when a certain treatment room 4A-4D of plural treatment rooms 4A-4D once occupies the accelerator 1 except intentional operation to release the occupation of the accelerator 1 or the occurrence of system failure.