Provided are a strap retention device that can improve the ability to reliably cut a strap, and an airbag device. A strap retention device includes an anchor having a retaining portion for retaining a first end of a strap, and a flat portion in contact with a back surface of the strap; a strap restraint member joined to the anchor for restraining movement of the strap in a width direction; a cutter for cutting the strap on the flat portion; a squib for applying a driving force to the cutter to move the cutter in a direction of the flat portion; and a housing accommodating the cutter and the squib and joined to the anchor.