A charged particle beam irradiation system in which the energy, Bragg peak, and irradiation depth of a charged particle beam, with which a patient is to be irradiated, can be checked in real time just before actual irradiation. Just before the actual irradiation, by providing a high-speed steering magnet with 100% current, a checking beam is intentionally hit into a beam damper. By using a dosimeter and a dose measuring device in front thereof, extraction beam intensity is measured. By using a multi-layer beam monitor, a dose distribution thereof is measured. Accordingly, just before the actual irradiation, the energy, Bragg peak, and irradiation depth of the charged particle beam, with which the patient is to be irradiated, can be checked accurately and in real time. When the beam has a desired dose distribution as a result of checking, continuously, extraction control is performed.
