A charged particle beam irradiation apparatus includes: an irradiation section configured to irradiate an irradiated body with a charged particle beam; a multi-leaf collimator configured to set an irradiation range of the charged particle beam which is irradiated from the irradiation section; an imaging section that is provided so as to be able to advance and retreat with respect to an irradiation axis of the charged particle beam which is irradiated from the irradiation section, between the irradiation section and the multi-leaf collimator, and directly images an opening portion of the multi-leaf collimator; and a drive section configured to move the imaging section between an imaging position corresponding to an irradiation area which includes the irradiation axis of the charged particle beam and a retreated position away from the irradiation area.