An exothermic warmer (1) includes an exothermic element (11) that is covered with a first cover sheet (21) and a second cover sheet (22). The first cover sheet (21) is a sheet that is air permeable and does not substantially limit an oxidation reaction. A water-retaining material (12) is provided so as to be at least partially in contact with the exothermic element (11). The exothermic warmer (1) satisfies the following conditions (A) to (C): (A) the difference between the internal temperature of the exothermic element and the highest surface temperature of the exothermic warmer is 10° C. or less; (B) the highest skin temperature obtained when the exothermic warmer is applied to human skin is 38° C. or more and 42° C. or less; and (C) the ratio of the amount (mg/cm2·10 min) of steam generated in 10 minutes after the start of the oxidation reaction to the mass (g/cm2) of the exothermic element takes a value of 50 or more and 250 or less.