A charged particle beam extraction system and method capable of ensuring higher safety when extraction of an ion beam is on/off-controlled during irradiation of the ion beam for treatment. The charged particle beam extraction system comprises a charged particle beam generator including a synchrotron, a range modulation wheel (RMW) for forming a Bragg peak width of a charged particle beam extracted from the charged particle beam generator, a gate signal generator for controlling start and stop of extraction of the charged particle beam from the charged particle beam generator in accordance with a rotational angle of the RMW, and an irradiation control/determination section for determining whether the start and stop of extraction of the charged particle beam is controlled at desired timing by the gate signal generator.
