a diagnostic unit 8 composed of such as a personal computer for diagnosing causes of the partial discharge and noise types and a display unit 9 for displaying results of diagnosis the partial discharge signal detectors 4 a 4 b and 4 c may be used as detecting antennas or internal electrodes included in the gas insulated apparatus a detection signal provided by the partial discharge signal detector is transferred through the broad band selector switch 5 and the amplifier 6 to the signal analyzer 7 the signal analyzer 7 processes the detection signal for signal analysis such as frequency analysis the diagnostic unit 8 receives data from the signal analyzer 7 and carries out a diagnostic procedure to determine the cause of a partial discharge and the type of noise results of diagnosis are displayed on the display unit 9 with such a configuration the partial discharge diagnosing system is able to accomplish the diagnosis in a very short time and to achieve the diagnosis of abnormal conditions occurred in the gas insulated apparatus through automatic monitoring a diagnostic procedure to be carried out by the diagnostic unit 8 will be described with reference to fig2 the signal analyzer 7 such as a spectrum analyzer analyzes a signal received from the partial discharge detectors 4 a 4 b and 4 c incorporated into the gas insulated apparatus a partial discharge is diagnosed by subjecting the analyzed partial discharge signal to diagnostic steps 1.