When an inner bag is inflated inside an outer bag, impact on an occupant received by an airbag is reduced. An inner bag (30) is inflated with gas supplied from an inflator (3). A gas exhaust port (31) is formed on the inner bag (30) and allows the gas to flow from the inner bag (30) in an occupant direction (E). An outer bag (20) accommodates the inner bag (30) and is inflated with the gas supplied from the gas exhaust port (31). A restriction member restricts the inflation of a portion of the inner bag (30) to change a direction of which the gas flows out from the gas exhaust port (31) to avoid the occupant direction. The restriction member breaks during the inflation of the outer bag (20) to release the restriction of the inflation of the inner bag (30).