An airbag device for a vehicle may include a main vent hole formed in an airbag cushion and configured to discharge an expanding gas therein, a cover provided to an outer side of the airbag cushion and configured to switch between a state in which the cover is spaced apart from the main vent hole by a given tensile force to open the main vent hole and a state in which the cover is closely adhered to the main vent hole to close the main vent hole, a tether configured to have one end portion connected to the cover and another end portion fixed in the airbag cushion and provide the tensile force to the cover through the main vent hole, and a tether guide.