AIRBAG DEVICE

[Problem] To provide an airbag device capable of controlling flow of gas discharged from an inflator. [Resolution Means] The airbag device is an airbag device that expands and deploys in a vehicle passenger compartment of a vehicle and restrains a passenger sitting in a first seat from a side, including: a cushion provided with a horizontal portion that deploys in a horizontal direction of the vehicle in an expanded and deployed state and a protruding portion that deploys in an upward direction of the vehicle from a center portion of the horizontal portion a diffuser that is secured inside the cushion that is open in the horizontal direction of the vehicle, closed in a downward direction of the vehicle, and partially or entirely closed in a direction toward the protruding portion; and an inflator that is secured to the first seat, provided inside the diffuser, and that discharges gas for expansion and deployment.