PURPOSE: To detect the rise of the temperature of a gas insulating apparatus in a metallic vessel with oscillation, by providing an expanding and contracting member having a large coefficient of thermal expansion in an oscillating material and bringing the tip of the expanding and contracting member into contact with another position of the oscillating material when the temperature attains a prescribed value.

CONSTITUTION: When the electric resistance rises to emit heat because of a defect of the contact between high voltage conductors 3 and a contact 4 which is the connection part between high voltage conductors 3, the temperature of an oscillating material 7 rises. Then, the temperature of an expanding and contracting member which is provided in the oscillating material 7 and has a large coefficient of thermal expansion rises, and the tip of the expanding and contracting member is brought into contact with an oscillating part in the opposite side or a projection by a prescribed raised abnormal temperature. As the result, the oscillating material 7 shows an oscillation characteristic different from the oscillating wave in the normal state by the shock applied from the external, thus detecting the occurrence of the abnormal rise of the temperature.