The objective of the present invention is to reduce the effect of the hysteresis of a scanning electromagnet so as to obtain a particle beam therapy system that realizes high-accuracy beam irradiation. There are included an irradiation management apparatus (32) that controls the scanning electromagnet (3), based on target irradiation position coordinates (Pi) of a charged particle beam (1b), and a position monitor (7) that measures measurement position coordinates (Ps) of the charged particle beam (1b). The irradiation management apparatus (32) has a command value creator (25) that outputs a control input (Io (Ir)) to the scanning electromagnet (3), based on the target irradiation position coordinates (Pi) and correction data (Ia) created on the basis of the measurement position coordinates (Ps), measured by the position monitor (7) in the preliminary irradiation in which the excitation pattern of the scanning electromagnet is the same as that of the main irradiation plan, and the target irradiation position coordinates (Pi).