Disclosed is an airbag apparatus for vehicles including a vent hole in an airbag cushion for discharging inflating gas. A cover is provided on an outer surface of the airbag cushion and is adjustable between a state where the cover is spaced apart from the vent hole to open it and a state where the cover comes into close contact with the vent hole to close it. A tether is connected at its first end to the cover and secured at its second end to an interior of the airbag cushion to impart a tensile force to the cover. A tether guide is provided on an inner surface of the airbag cushion to support the tether, and a sealing means is provided between the vent hole and the tether guide to support the tether, the tether passing through the sealing means.