In the particle beam therapy, therapy is implemented by irradiating a charged particle beam (referred to as a particle beam, hereinafter) onto a diseased site, which is a therapy subject, so as to cause damage to diseased tissue; it is required to give a sufficient dose to the diseased tissue, which is an irradiation subject, and suppress a dose to the peripheral tissues. Accordingly, the irradiation dose and the irradiation coverage (referred to as an irradiation field, hereinafter) is controlled in accordance with the shape of the irradiation subject. With regard to an irradiation subject whose position and shape change with breathing, a respiratory phase is measured, and then a particle beam is irradiated onto the irradiation subject at a respiratory phase when the position and the shape are stabilized (for example, refer to Patent Documents 1 and 2).
Meanwhile, the plant of an accelerator, which is a beam supply source in particle beam therapy, is gigantic; therefore, in general, even at an institution having a plurality of treatment rooms, the courses of a particle beam outputted from a single accelerator are switched so that a particle beam is supplied to each treatment room. Accordingly, in order to enable a great number of patients to undergo the therapy, there have been proposed a particle beam therapy system in which the control of course-switching electromagnets is contrived in such a way that the time required to switch the courses of a particle beam is shortened (e.g., refer to Patent Document 3) and a particle beam therapy system in which the respiration is induced in such a way as to be in phase with the operation cycle of an accelerator or the like so that the therapy time is shortened (e.g., refer to Patent Document 4).