SIDE AIRBAG DEVICE AND VEHICLE SEAT PROVIDED THEREWITH

[Problem]To provide: a side airbag device capable of quickly and properly restraining a passenger in the initial stage of deploying an airbag; and a vehicle seat provided with the side airbag device. [0002] [MEANS FOR SOLVING THE PROBLEM] [0003] The airbag is provided with a main chamber that deploys toward the front of the vehicle and a pre-chamber that houses the inflator and begins to deploy ahead of the main chamber in the vehicle width direction to the inside of the main chamber. Here, the main chamber is demarcated into a front region and a rear region by a demarcation. The boundary area between the main chamber and the pre-chamber is provided with a front vent that directs the expanding gas from the pre-chamber to the pre-chamber front area and a rear vent that directs the gas to the rear region.