Airbag device

An airbag device to be applied to a vehicle provided with A to C pillars, a door, and a side sill includes an airbag, a collision mode predictor, and a pressure controller. The airbag is deployed from a container to be disposed on a lower side of the side sill to a region on a vehicle-widthwise outside of a side surface of a vehicle body including the door. The airbag includes a first air chamber disposed mainly in front of the B pillar after being deployed and a second air chamber disposed mainly behind the B pillar after being deployed. The collision mode predictor predicts a collision mode of an object with the vehicle. The pressure controller increases or reduces at least either of internal pressures of the first air chamber and the second air chamber independently of the other, based on the predicted collision mode.