An airbag device includes a movement obtaining unit, an airbag, and an airbag controller. The movement obtaining unit is configured to obtain a movement of an occupant in an automobile. The airbag is deployable with different thicknesses into a gap between the occupant and a side portion of the automobile. The airbag controller is configured to restrict the thickness of the airbag that deploys toward the gap so that the airbag is inserted into the gap, if the airbag controller determines that the gap is smaller than a predetermined value on the basis of the movement of the occupant obtained by the movement obtaining unit.