An airbag comprises an airbag main body formed into a bag by a front panel and a rear panel, a vent hole formed on the rear panel, a vent cover that is attached to an outer surface of the rear panel and opens and closes the vent hole, a tether provided on the vent cover, a vent patch attached to an inner surface of the rear panel, and a tether cover attached to the inner surface of the rear panel, overlapping the vent patch, wherein: the tether is pulled from a slit formed near the vent hole of the rear panel into the interior of the airbag main body and then inserted through an area between the vent patch and the tether cover.