Problem to be solved: to prevent the erroneous operation from occurring, and to detect the current at the time when the current is energized in the air, and to quickly interrupt the heating of the heating elementSolution: the main case 15 in which the heating element 20 is sealed and the side case 34 in which the temperature sensitive portion of the shut-off means 35 is housed is arranged in parallel while spaced apart by a predetermined distance, while the main contact part 40A of the heat transfer member 40 made of a heat conductive material is superposed on the heating element Since the side contact portion 40B is closely adhered to the outer surface of the sub case 34 in the state where the auxiliary contact portion 40B overlaps with the temperature sensitive portion, the heat transfer member 40 is quickly absorbed into the water W even when heat is supplied from the heating element 20, and is almost the same as the water temperatureWhen the gas is energized, a large amount of heat flows into the sub case 34 through the heat transfer member 40 from the main case 15, and the temperature sensitive portion rapidly rises to the abnormal temperature, that is, it detects the electric current in the air early, and the outer surface of the main case 15. At a relatively low temperature, the energization of the heating element 20 is interrupted.Diagram【課題】誤作動を阻止しながら、気中通電状態となったとき、早期にこれを検出して発熱体20への通電を迅速に遮断する【解決手段】発熱体20が密閉収納された主ケース15と、遮断手段35の感温部が密閉収納された副ケース34とを一定距離離して平行に配置する一方、熱伝導材料からなる伝熱体40の主密着部40aを発熱体20に重なり合った状態で主ケース15の外面に、副密着部40bを感温部に重なり合った状態で副ケース34の外面に密着させたので、水温制御時、伝熱体40は発熱体20から熱が流入しても水Wに速やかに吸熱されてほぼ水温に保持され、誤作動が確実に阻止される一方、気中通電時には主ケース15から伝熱体40を通じて副ケース34に大量の熱量が流入するため、感温部は速やかに異常温度まで上昇、即ち早期に気中通電を検出し、主ケース15の外面が比較的低い温度のときに発熱体20への通電が遮断される。【選択図】図2
