[Problem] To expand and deploy a hood-shaped airbag in a reliably sandwiched condition between the top of a shoulder of a seated occupant and a seatbelt in a normal set condition during a collision, and reduce injury to the occupant by a device other than an airbag such as a seatbelt or the like.
[Resolution Means] An airbag device 11 contains an airbag 12 and inflator 13 integrally covering the head 2a and a side portion of a seated occupant 2. The airbag 12 in a flat condition prior to folding has a plurality of chambers 12c demarcated in a longitudinal direction. The chamber 12c has a head protecting chamber 12ca stored in an upper portion of a backrest portion 1b of a seat 1 and a pair of side protecting chambers 12cb stored in opposing positions separated in a vehicle width direction on both left and right sides of the backrest portion 1b. At the time of expansion and deployment, the side protecting chamber 12cb expands and deploys between the seatbelt 3 and occupant 2, and thus the airbag 12 is configured such that a space S is formed between the occupant 2 and airbag 12 deployed at a position where the seatbelt 3 passes.