A particle beam therapy system comprises a treatment table (30), a treatment table control unit (61) and an irradiation control unit (60) configured to output an instruction for controlling the treatment table control unit, an accelerator (1) and a scanning electromagnet (7). After the treatment table control unit has controlled the treatment table (30) so as for a patient isocenter which is a reference position of an affected area of a patient to move to a position of an irradiation isocenter (IC2) which is set at a position which is closer to an irradiation nozzle (4) than an equipment isocenter (IC1) which is a reference of positional relation of the irradiation nozzle (4) and the treatment table (30), the irradiation control unit (60) outputs an instruction for irradiating the patient with a particle beam.
