An airbag device includes: a bag body that is deployed by internal pressure rising as a gas is supplied into the bag body; and a gas pressure adjustment portion that is provided on the bag body so as to be able to release the gas from the inside of the bag body during a deployed state of the bag body, and that is set so that the amount of the gas released from the bag body in the deployed state to an inward side in a vehicle width direction is larger than the amount of the gas released from the bag body in the deployed state to an outward side in the vehicle width direction.