An airbag device comprises: an airbag including a head-protecting cushion that protects the head of an occupant by being deployed from an upper portion on the left or right side of a vehicle seat; and an inflator that supplies an inflation gas to the airbag. The head-protecting cushion comprises: a first chamber that protects an area near one side of the head of the occupant; a second chamber connected to the first chamber and which protects the front of the head of the occupant; a third chamber connected to the second chamber and which is deployed to span from the front of the head of the occupant to the other side of the head of the occupant; and a fourth chamber connected to the third chamber and which is deployed in an area near the other side of the head of the occupant.