An airbag device installed into an instrument panel including a lid portion configured to be torn and a lid-side peripheral wall portion provided to stand on an outer periphery of the lid portion. The airbag device includes: an inflator; an airbag so as to be inflated and deployed in a bag shape by the gas introduced from the inflator; and an outer bag formed of a sheet-like member to be sewn into a three-dimensional shape having an outer-bag-side bottom and an outer-bag-side peripheral wall portion provided on an outer periphery of the outer-bag-side bottom, the outer-bag-side bottom being secured to the inflator, the outer-bag-side peripheral wall portion surrounding the folded airbag and being disposed so as to be sandwiched between the airbag being inflated and deployed and the lid-side peripheral wall portion.