A cover member (18) is formed of a pliable fabric material having a plurality of polymer fibers, and is configured to maintain the shape of the airbag by mutual fusion of at least part of the polymer fibers. The cover member (18) is configured to have a high stiffness portion (25) of higher stiffness than other portions of the cover member, as a result of partial overlaying of the pliable fabric material in more folds than at other portions.