A heat implement (1) comprises a heating element (11) coated with a first coating sheet (21) and a second coating sheet (22). The first coating sheet (21) has a gas permeability and thus substantially does not suppress an oxidation reaction. A water retaining material (12) is provided in a state of being at least partially in contact with the heating element (11). The heat implement (1) satisfies the following requirements (A) to (C). (A) The difference between the inner temperature of the heating element and the maximum temperature on the surface of the heating implement is not more than 10 DEG C. (B) When the heating implement is applied to the skin of human body, the maximum temperature of the skin is 38-42 DEG C inclusive. (C) The ratio of the amount (mg/cm2·10 min) of vapor generated within 10 minutes after the initiation of the oxidation reaction to the mass (g/cm2) of the heating element is 50-250 inclusive.本發明之發熱器具(1)係利用第一被覆片材(21)與第二被覆片材(22)被覆發熱體(11)而成。第一被覆片材(21)為具備不會實質上制約氧化反應之透氣性之片材。保水材(12)係以至少一部分接觸於發熱體(11)之方式配備。發熱器具(1)滿足以下之(A)~(C)之條件。(A)發熱體之內部溫度與發熱器具之表面之最高溫度的差為10℃以下。(B)對人體皮膚應用發熱器具時之皮膚之最高溫度為38℃以上且42℃以下。(C)氧化反應開始起10分鐘產生之水蒸氣量(mg/cm2．10min)/發熱體之質量(g/cm2)之值為50以上且250以下。
