PURPOSE: To improve control sensitivity of a thermal switch in relation to a temperature change of a base plate on which equipment is installed, by fitting a hydrogen storage alloy storing a large quantity of a hydrogen gas inside a bellows being a movable part of the thermal switch.

CONSTITUTION: When a temperature of equipment 8, namely, a temperature of a base plate 1 is in the vicinity of the lower limit of a required temperature range, a temperature of a hydrogen storage alloy 4 in a bellows 3 is low so that the hydrogen storage alloy 4 stores a large quantity of a hydrogen to reduce a quantity of the hydrogen gas 5 in the bellows 3. The bellows 3 therefore is not extended and the base plate 1 is separated from a heat radiating plate 2 by means of a spring 6. When the temperature of the equipment 8, on the contrary, is in the vicinity of the upper limit of the required temperature range, the temperature of the hydrogen storage alloy 4 in the bellows 3 is high so that a hydrogen storing rate thereof decreases, the hydrogen gas 5 is discharged from the alloy 4, and gas pressure thereof is increased to extend the bellows 3. Consequently, the base plate 1 is brought into contact with the heat radiating plate 2 so that a heat quantity in the equipment 8 is introduced to the heat radiating plate 2.