A particle beam irradiation apparatus comprises a particle beam shielding member which shields a part of a particle beam which is scanned, a prompt signal detector which detects a prompt signal which is generated when the particle beam which is scanned collides with the particle beam shielding member and a signal comparison device which predicts and obtains a generation pattern of a prompt signal which is generated with a predetermined scanning pattern and stores as a signal time pattern for comparison, wherein the signal comparison device detects an abnormality of scanning of a particle beam or the particle beam shielding member by comparing a detected signal time pattern which is a time pattern of a signal which is detected by the prompt signal detector to a signal time pattern for comparison which is stored.
