AIRBAG DEVICE AND OCCUPANT PROTECTION DEVICE

An airbag device includes an inflator that is installed in an upper part of a vehicle seat, and that generates gas in an event of a vehicle collision, an airbag to which the gas from the inflator is supplied, and is inflated and deployed from the upper part of the vehicle seat toward a front side of the vehicle seat, and a diffuser that distributes the gas to the airbag. The diffuser includes a connecting portion that is connected to the inflator, and a plurality of branching portions that each branch from the connecting portion and connect to the airbag. The diffuser includes a silencing portion in at least the branching portions. The silencing portion reduces sound pressure of the gas.