To provide a temperature-sensitive sensor that is excellent in temperature sensitivity by utilizing an ionic liquid.

A non-return type temperature-sensitive sensor is composed so that an electrolyte being solid at a normal temperature is used as a temperature-sensitive body and an electrode is made easily soluble in a molten electrolytic solution. The non-return type temperature-sensitive sensor is attached to equipment to be protected. Operation of the equipment to be protected is stopped on the basis of a drop in resistance value of the temperature-sensitive sensor due to electrolyte melting caused by a temperature rise of the equipment to be protected and elution of an electrode material into the molten electrolyte.