SIDE AIRBAG DEVICE

[Problem] To provide a side airbag apparatus capable of efficiently improving passenger protection performance and passenger restraining force. [Resolution means] A side airbag apparatus includes: a cushion which is bag shaped, wound, or folded in a storage form; a holding plate with the cushion attached thereto; and an inflator which is embedded in the cushion and attached to a side frame along the side of a seat back of a seat together with the cushion and the holding plate The holding plate includes: a base part formed between the cushion and the side frame ; and a side wall part which extends in the front-back direction of the vehicle in front of the side frame in the front-back direction of the vehicle and supports the expanded and deployed cushion from the side.