PURPOSE: To prevent residual magnetism and reduce wear of steel rope or the like, by integrally providing a de-exciter on the outside of an exciter.

CONSTITUTION: A de-exciter 6 consisting of de-exciting coils 6a, 6b is provided integrally on the outside of an exciter 2, and an alternating current iAC is applied to the de-exciter 6, so that the residual magnetism in a steel rope 1 is demagnetized by the polarity conversion of the alternating current. Therefore, abnormal wear of steel rope 1 or sheave may be prevented. Besides, a flaw detection signal due to magnetization of the steel rope 1 is detected by a coil 3, and is amplified 4 and supplied into a recorder 5.