An airbag device includes an airbag cushion unit inflatable with working gas introduced thereto, one or more variable vent units protruding outward from the airbag cushion unit and including a hollow portion communicating with an inner portion of the airbag cushion unit, and one or more tether units having one portion shaped to surround the variable vent unit and the other portion fixed to an outer portion of the airbag cushion unit, and configured to tighten and close the variable vent unit in response to the airbag cushion unit being inflated.