The present invention is provided with an invariant period determination unit (1) for determining whether the operation of an object under detection is in an invariant period; a correction parameter creation unit (3) for creating from an observation signal obtained by observing operation sound during the invariant period a correction parameter for correcting an observation signal from a time period other than the invariant period; a feature extraction unit (4) for extracting a feature amount for the operation sound of the object under detection in the time period other than the invariant period on the basis of the observation signal for the object under detection in the time period other than the invariant period and the correction parameter if a determination is made that the operation is in the time period other than the invariant period; and an abnormal sound determination unit (5) for determining whether an abnormal sound is being produced in the object under detection on the basis of the extracted feature amount.
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