PURPOSE: To elongate action time of a thermal overload relay.

CONSTITUTION: Plural thin plates 6 of thermal conductor are laminated and held between a bimetal 4 and a heater 5 for composing a heater element of a thermal overload relay. The bimetal 4 is thus heated after the thin plates 6 are heated by the heater 5, so time till the bimetal gets to a specified action temperature delays to elongate action time of the termal relay. This action time can be regulated as desired by changing the number or thickness of the thin plates 6.