PARTICLE BEAM IRRADIATION APPARATUS

The particle beam irradiation apparatus includes: an irradiation unit configured to radiate a particle beam; a first detection unit configured to detect first particles; a second detection unit configured to detect second particles; an image forming unit configured to form an observation image based on a first signal obtained by the detection of the first particles, which is performed by the first detection unit, and to form an observation image based on a second signal obtained by the detection of the second particles, which is performed by the second detection unit; and a control unit configured to calculate a brightness of a first region in the formed first observation image and perform a brightness adjustment of the first detection unit based on a first target brightness as a first brightness adjustment when the brightness of the first region is different from the first target brightness.