PURPOSE: To simplify the waveform processing to shorten the fetching interval of data, by providing a vibration monitor unit in vibration analysis of a rotary machine to make it possible to take in displacement signals from axes different in rotation frequency.

CONSTITUTION: Displacement signal Xi(t) generated by axia vibration of a rotary machine and frequency signal fNi(t) synchronized with the rotation frequency are supplied to vibration monitor units 5aW5n. Frequency fN synchronized with the rotation frequency, frequency fMON other than the rotation frequency, amplitude AN of rotation frequency synchronizing components, and amplitude AMON of rotation frequency asynchronizing components which are obtained in units 5aW5n are input to waveform synthesizing circuits 6aW6n and are synthesized into signals S1WSn respectively and are supplied to waveform processing unit 3 through A/D converters 1aW1n and buffer memory 4. Then, unit 3 subjects these signals to a prescribed processing to obtain an objective value.