PURPOSE: To detect an abnormality of an object being inspected accurately and speedily through a statistical operational processing, by removing disturbances such as vibrations and sounds from vibration sources other than the object.

CONSTITUTION: The detection signals obtained by a vibration detector 1 such as a vibration pick-up are fed into a plurality of frequency analizing sections 301... 30n adapted to pass only frequency components within frequency bands different from each other. Over an inspection time consisting of a plurality of sampling periods, a maximum peak value of each frequency component is detected once for each sampling period. The obtained maximum peak value is analog-digital converted at 11 and stored in an operational control section 27. Moreover, the stored maximum peak values from which disturbance data are removed are compared with a set value which is previously set, thereby to judge an object being inspected to be abnormal or not.