A beam scheduler adds the maximum allowable waiting time until a beam is allocated to an irradiation chamber corresponding to an irradiation request when the irradiation request is received from one irradiation chamber of a plurality of irradiation chambers A to D adds the irradiation request to the end of the order of a waiting list determines whether or not the predicted waiting time until the beam is allocated to the one irradiation chamber exceeds the maximum allowable waiting time and advances the order of the irradiation request on the waiting list, thereby allocating the beam to the irradiation chamber corresponding to the top irradiation request in the order of the waiting list, if it is determined that the predicted waiting time exceeds the maximum allowable waiting time.
