A head-protecting airbag according to the present invention is normally folded and housed in an upper edge of windows inside a vehicle, and includes a gas admissive portion inflatable with inflation gas from inflator and a non-admissive portion admitting no inflation gas. The gas admissive portion includes a shielding portion for covering the vehicle's interior side of the windows upon deployment of the airbag. The shielding portion includes a plurality of vertical chambers each of which is located vertically upon deployment of the airbag, and at least one horizontal chamber which is located along longitudinal direction of the vehicle upon deployment of the airbag. The horizontal chamber is located between at least one neighboring pair of the vertical chambers in the vicinity of vertically middle position of the pair of the vertical chambers, thereby communicating the pair of the vertical chambers.