PURPOSE: To previously prevent a vacuum apparatus from accidents with a simple configuration by incorporating a radiometer into the inside of the vacuum case of the vacuum apparatus and supervising the degree of vacuum by the rotation of the radiometer.

CONSTITUTION: A radiometer 2 is set up within the vacuum range of a vacuum interrupter 1 and the rotation of the radiometer 2 is detected by a detector 3 to detect the degree of vacuum. Since the vacuum range in the interrupter 1 is kept at a high degree of vacuum, the radiometer 2 does not rotate even if the heat from a heating element of a lead rod arranged close to the radiometer 2 is irradiated to the radiometer 2, and starts to rotate only when the degree of vacuum is reduced and air is penetrated into the vacuum range. Consequently, the reduction of the degree of vacuum can be detected by supervising the radiometer 2, previously preventing a vacuum apparaus from serious accidents.