The airbag apparatus is provided with a retainer that includes a hold-down portion for attachment of a periphery of a gas inlet of an airbag to the case, a cover wall surrounding an inflator body, deflectors and catches. The cover wall includes a plurality of outlet ports for releasing inflation gas exited discharge ports of the inflator body radially. The deflectors deflect the inflation gas exited the outlet ports in a range of angle from a direction orthogonal to an axis of the inflator body to a downward direction extending toward the hold-down portion. The catches capture residual particles contained in the inflation gas when the gas deflected by the deflectors hit them.