SIDE AIRBAG DEVICE

A side airbag device includes: a main bag which is an airbag deployed between a passenger seated on a seat and a side wall portion of a vehicle, the airbag being configured to expand by gas supply when a vehicle side collision occurs; and a sub bag deployed between a side frame on a vehicle outer side in a seat back of the seat and the passenger, the sub bag being configured to expand by supplying gas and push a waist portion of the passenger forward from backward, prior to deployment of the main bag, when the vehicle side collision occurs.