A tension member for an airbag, and an airbag device are provided in each of which the tensile force is controlled continuously with a simple configuration. An airbag device includes an airbag that is normally folded and is inflated and deployed in a case of an emergency, an inflator for supplying gas into the airbag, a retainer for retaining the airbag and the inflator, and a tension member that controls a shape or a function of the airbag by using tension. The tension member for an airbag includes two end portions connected to respective portions of the airbag that are movable relative to each other when the airbag is inflated and deployed, a widened portion provided between the two end portions, and a breaking section provided in the widened portion in such a manner as to extend in a direction of widening of the widened portion and configured to break depending on a magnitude of tension applied between the two end portions.