To provide an airbag device capable of sufficiently inflating and deploying an airbag body even if an inflator of a low output is used.

This airbag device has the airbag body 6 which can be wholly inflated and deployed into a bag shape, and the inflator 5 jetting burned compressed gas to inflate and deploy the airbag body 6. The airbag body 6 has two side-face deploying chambers 21 for forming both side faces when the airbag is inflated and deployed, a traverse deploying chamber 22 inflated and deployed to separate the two side-face deploying chambers 21 when the airbag body 5 is inflated and deployed, a main constricting chamber 23 formed between the two side-face deploying chambers 21 when the airbag body 6 is inflated and deployed, and an outside air inflow hole 24 for making outside air flow in the main constricting chamber 23. The inflator 5 jets the burned compressed gas into the side-face deploying chambers 21 and the separating chamber 22.