A particle beam irradiation system includes a particle beam irradiation apparatus, which is free of a gantry structure, having a particle beam irradiator for irradiating an affected area of a patient with a particle beam, the particle beam irradiator being housed in a chamber, a CT scanner installed in the chamber, for positionally confirming the affected area of the patient, a drive unit for moving the patient from a detection range to an irradiation range, a patient fixing device for fixing the patient in position, the device being mounted on the drive unit for rotation, and a housing unit having a structure housing the drive unit with the patient fixing device mounted and the CT scanner, the housing unit being rotatable about an axis perpendicular to a plane including a direction in which the particle beam is applied and a direction in which the drive unit moves.