Airbag device

An airbag device for protecting an occupant seated on a vehicle seat of a vehicle from an impact by deploying and inflating an airbag with an inflation gas in a case where the impact is applied to the vehicle from an obliquely front outer side of the vehicle seat or in a case where it is predicted that the impact is to be applied to the vehicle, wherein

• when in a width direction of a seatback of the vehicle seat, a side closer to a central portion of the seatback in the width direction is defined as an inner side and a side farther from the central portion of the seatback in the width direction is defined as an outer side, the airbag includes
• a main inflation portion that is to be deployed and inflated at the outer side of an upper body of the occupant, and
• an auxiliary inflation portion that is disposed at a position adjacent to the inner side of the main inflation portion and is to be deployed and inflated at an obliquely front outer side of a head portion of the occupant by the inflation gas passing through the main inflation portion,
• the auxiliary inflation portion is joined to the main inflation portion in a joining area, in a state of being in communication with the main inflation portion,
• the auxiliary inflation portion includes an annular side portion constituting an outer peripheral portion, an outer main body portion surrounded by an outer edge portion of the annular side portion, and an inner main body portion surrounded by an inner edge portion of the annular side portion,
• in the auxiliary inflation portion whose deployment and inflation are completed, a maximum dimension in a facing direction in which the outer main body portion and the inner main body portion face each other is set to be smaller than a dimension in a direction orthogonal to the facing direction, and
• the outer main body portion is joined to the main inflation portion as the joining area of the auxiliary inflation portion.