An airbag device, comprising: a gas generation device that is operable to generate gas; and an airbag that includes: a first chamber portion that is disposed at a vehicle front side of a vehicle seat on which a vehicle occupant sits, the first chamber portion being inflated due to gas generated by the gas generation device being supplied into the first chamber portion, a second chamber portion that is inflated due to gas generated by the gas generation device being supplied into the second chamber portion and that is disposed adjacent to the first chamber portion in a vehicle width direction, and a connection portion.