This invention provides a heating device ensuring sufficient adhesive force, even when it is removed from clothing and then reattached to different clothing. The heating device of the present invention comprises a bag unit 2 containing an exothermic composition A including an oxidizable metal that can generate heat by contact with air, one surface of the bag unit 2 being air-permeable an adhesive layer 3 formed on the other surface of the bag unit 2 a first release sheet 4 provided on the adhesive layer 3 to cover the adhesive layer 3 and a second release sheet 5 provided on the first release sheet 4 to cover the first release sheet 4, wherein the first release sheet 4 has a release portion 41 and a residual portion 42 when the second release sheet 5 is removed from the first release sheet 4, the release portion 41 is removed together with the second release sheet 5 and the residual portion 42 remains on the adhesive layer 3.
