An abnormality diagnosing system and method for high voltage power apparatus wherein a plurality of detectors for detecting abnormalities of the high voltage power apparatus and providing outputs indicative thereof are disposed to detect predetermined phenomena indicative of at least an insulation abnormalituy, power supply abnormality and foreign matter among abnormalities existing inside of the high voltage power apparatus. A monitoring arrangement responsive to the outputs of the detectors provides at least one of an output and display of the kind of abnormality detected.