A side airbag for enhancing protection of a shoulder area of a vehicle occupant having an airbag (10) which deploys beside an occupant toward the vehicle front, and an inflator (20). Before deploying, the airbag (10) is in a state having: an overlapping part (12) formed by overlapping a portion near an end part by accordion-folding or rolling; a folded-back part (14) on an inner side of the overlapping part (12) in a vehicle width direction and extended toward the front of the vehicle and folded back toward the rear of the vehicle; and a bent part (16) formed by bending a portion of the folded-back part (14), protruding from the overlapping part (12) toward the front of the vehicle toward an outer side in the vehicle width direction and covering at least part of the overlapping part (12).