A heating element (10) according to the present invention comprises a structure including a heating layer (11) that includes an oxidizable metal (21), a desiccant (22), and water, and a fiber layer (12) with a maximum water holding rate of 500% or less, wherein the content of water in the heating layer (11) is 10 to 60% by mass, and the hardness of the structure measured under the following condition is 10 to 200 g/mm. (Condition) A test piece cut from the structure so as to have a square surface with a side length of 2 cm and a cylindrical pipe with an inner diameter of 1 cm are prepared, and the test piece is arranged on the cylindrical pipe so that the central part of the square surface and the central part of the cylindrical pipe overlap. Then, using a cylindrical plunger with a diameter of 1 mm, a rupture test is performed by lowering the distal end of the plunger from the top of the test piece to the internal center of the cylindrical pipe at a speed of 5 cm/min. In this rupture test, the maximum value of the rupture stress until the test piece ruptures is detected and is treated as a (g). The hardness is found by dividing a by the average thickness b (mm) of the heating layer (11).
