An airbag device equipped with an airbag having a reduced volume. An airbag inflated and expanded, by supplied gas, from a state folded in the rear of an instrument panel with respect to the vehicle's front-rear direction has an outer bag for restraining the upper body of a vehicle occupant from the front side in the vehicle's front-rear direction and also has a reaction force support tube inflated and expanded, by supplied gas, at the front on the inner side of the outer airbag. An inflator supplies gas to each of the outer bag and the reaction force support tube. When the outer bag restrains the upper body of the vehicle occupant, gas discharge from the reaction force support tube is suppressed by a one-way valve and the pressure in the reaction force support tube is maintained at a pressure higher than the pressure in the outer bag.