PURPOSE: To improve accuracy in judgement of abnormal temperature by arranging temperature detectors on the outer wall face of an electric machine container respectively at positions where it is subjected to heating and where it is not subjected to heating then judging whether the temperature is abnormal or not based on the difference of detected temperature.

CONSTITUTION: A conductor 3 for passing a large current is contained in the metallic container 2 for a gas insulated switchgear, where a temperature detector 5 is arranged on the outer wall face of the container 2 at a position corresponding to the joint 4, i.e., a heating portion, of the conductor 3 and another temperature detector 6 is arranged on the outer wall face at a pocket section 2C where there is no heating portion, and both temperature detectors 5, 6 are connected with a judging section 10. Assuming the difference of temperature detected through the temperature detector 5 at the heating side and the temperature detector 6 at the non-heating side is T, abnormality of the temperature T can be judged accurately by previously grasping the relation between the actual temperature at the joint under normal power supply and the temperature of the metallic container as a data base.