For example, even when an occupant is seated offset in a left-right direction, an airbag is reliably expanded and deployed. An airbag device contains: an airbag that protects at least a side portion of a shoulder region, upper arm region, and chest region of an occupant seated on a vehicle seat; and an inflator that supplies gas to the airbag. The airbag has a pair of side part protection chambers that are housed on at least both left and right sides of the vehicle seat. The side part protection chambers, when expanded and deployed, expand and deploy forward independently from both left and right sides of the vehicle seat. A pair of the inflators are provided to allow gas to be supplied to each side part protection chamber, and the ignition timing of the inflators can be controlled separately.