To provide an airbag device capable of laterally equally inflating an airbag body in operation.

This airbag device S is arranged in a seat part so as to regulate the forward movement of an occupant seated on the seat in operation, and has an airbag 20 and an inflator 41. The airbag has the airbag body 21 having an upper wall 22 and a lower wall 26, and an inner bag 30 arranged in the airbag body so as to wrap the inflator 41 and having an outflow port 32a for making inflating gas from the inflator 41 flow out to the airbag body 21 side. The inner bag 30 is arranged by respectively opening the outflow port 32a upward on both right-left sides on the rear side. A gas jetting port 47 for supplying the inflating gas into the inner bag in the inflator, is arranged so that the inflating gas flowed out of the right-left outflow ports can equally flow out of the right-left outflow ports.