AIRBAG CUSHION

The present invention is a side airbag device (20) housed in a vehicle seat, having: an airbag cushion (30) that restrains an occupant by expanding and deploying; and an inflator (32) that supplies expansion gas to the airbag cushion. Furthermore, the airbag cushion includes: an inflator housing region (134) that houses the inflator; a main chamber region (135) that primarily contributes to restraining an occupant; and a skeletal region (136) that is connected to the inflator housing region and deploys in a rod shape prior to the main chamber. Furthermore, a first vent hole /144) that discharges the expansion gas into the main chamber is formed in the skeletal region.