PURPOSE: To predict the stop of a rotating machine before it stops actually.

CONSTITUTION: A diagnostic system comprises pickups 1A-1H for detecting vibrations of a rotating machine and outputting analog signals, and A/D convertors 2A-2H for converting the analog signals into digital signals. A vibration frequency analyzer 3 is connected to the A/D convertors 2A-2H and the frequencies and vibration waveforms of the digital signals are analyzer therein. Furthermore, a computer 4 is connected to the vibration frequency analyzer 3, analysis results of the frequencies and vibration waveforms are stored to a memory one by one and, with the stored analysis results compared with the normal values of previously stored frequencies and vibration waveforms, the normality or abnormality of a rotary device is discriminated. And, when it is discriminated that the rotating machine is abnormal, the alarm is given, and the time for the machine to stop is predicted.