A heat generation device (1) has a heat generation body (20) received in a stretchable bag body (10) having air permeability. The heat generation body (20) has a first surface (23) located on the near side to a wearers skin and having air permeability, a second surface (24) located on the far side from the wearers skin, and a heat generation section (21) placed between the first surface (23) and the second surface (24). In a plan view of the heat generation device (1), it is preferable that, in a portion where the stretchable bag body (10) and the heat generation body (20) are superposed on each other, a part of the heat generation body (20) be fixed to a part of the inner surface of the stretchable bag body (10).
