The purpose of the present invention is to provide a heat generator that contains a volatile component and in which the volatile component is stably maintained during storage, the volatile component is prevented from adhering to a heat-generating section, and it is possible to achieve an excellent warming effect during use. This heat generator comprises a heat-generating section (1), an accommodation body (2) for accommodating the heat-generating section (1), an adhesive layer (3) provided to an attachment surface side of the accommodation body (2), and a release sheet (4) provided to the attachment surface side of the adhesive layer (3). As a result of including a volatile component in the adhesive layer (3) and respectively providing gas barrier layers (211), (41) to a first packaging material (21) constituting the attachment surface side of the accommodation body (2) and to the release sheet (4), it is possible to stably maintain the volatile component within the adhesive layer (3) during storage. It is thereby possible to prevent the volatile component from adhering to the heat-generating section (1) during storage and to achieve an excellent warming effect during use.