In a charged particle irradiation system, forming a uniform dose distribution is required by irradiating a moving irradiation object through beam scanning and energy stacking. The charged particle irradiation system includes an ion beam generator 1 from which an ion beam is extracted with a target beam current value thereof set an irradiation nozzle 21 having scanning magnets 23, 24 and an energy filter 26, the irradiation nozzle 21 for irradiating an irradiation object with the ion beam and an irradiation object monitoring unit 66 for measuring a position of the irradiation object and outputting signals that vary with time according to displacement of the irradiation object. The charged particle irradiation system determines extraction timing of the ion beam based on the signal outputted from the irradiation object monitoring unit 66 and sequentially changes energies of the ion beam to thereby perform a repainting irradiation with each of the energies.
