A head-protecting airbag of the present invention includes an airbag body having a gas admissive portion for covering side windows upon deployment, and a belt for pulling a lower part of the airbag body toward exterior of vehicle during deployment. The gas admissive portion includes an initially inflatable portion located along upper edge of the airbag body, and a protective portion located at side of an occupant's head. The protective portion includes a main cell that inflates thickly when a temporary joint joining the inner wall and the outer wall is separated. The airbag body folded together with the belt and housed above the windows is provided, in the initially inflatable portion, with a folded and piled portion folded and piled in vertical direction, and below the folded and piled portion, with a roll-folded portion rolled toward exterior of vehicle from lower edge side. The head-protecting airbag of the present invention is developed smoothly and stably in a clearance between the side windows and occupants' heads, even if the clearance is narrow.