A load on the shins when a knee airbag is deployed by inflating in a state in which the knees of an occupant are proximate to an airbag door or suchlike is moderated. Inside a knee airbag, an upper tether and a lower tether are disposed to sandwich an inflator from above and below. First opening portions and second opening portions for letting gas flow through up and down are alternatingly formed in the upper tether and the lower tether. The second opening portions are formed as circular holes with smaller diameters than the first opening portions. The second opening portions are disposed at positions opposing the knees of a small occupant in a sitting state.