A heat generating device 1 has a heat generating element 20 enclosed in an air-permeable stretch bag 10. The heat generating element 20 includes an air-permeable first side 23 adapted to be located proximal to the skin of a wearer, a second side 24 adapted to be located distal to the skin of a wearer, and a heat generating member 21 interposed between the first side 23 and the second side 24. It is preferred that a part of the heat generating element 20 is fixed to a part of the inner side of the stretch bag 10 in the overlap between the stretch bag 10 and the heat generating element 20 in a plan view of the heat generating device 1.
