PURPOSE: To make it possible to clearly detect the abnormality in gas insulating machinery, by cumulating the signal based on the vibration of metal fine particles regardless of the cycle of voltage of a power source to emphasize the same.

CONSTITUTION: The vibration in gas insulating machinery 1 detected by a vibrometer 2 is amplified by an amplifier 3 and taken in a sampling apparatus 5 at every predetermined short-time interval. The output signal of the amplifier 3 at each time taken in the sampling apparatus 5 is converted to a digital signal by an A/D converter 6 to be inputted to an operator 8 to be cumulated and stored therein. The operator 8 operates an average value at every predetermined time interval at each time when the number of cumulation times reach a predetermined value and the operation result is applied to a judge device 9 and a display device 10.