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Ferromagnetic materials are widely used for various artificial products such as cars, trains, ships. Because of its mechanical property, iron steel is most popular in use for frame materials. Nondestructive testing of iron steel is an extremely important way to maintain their mechanical reliability. As is well known fact, the Barkhausen signals are emitted from only the ferromagnetic materials having magnetic domain structures. Also this signal varies depending upon their past mechanical as well as radioactive stress histories. In the present paper, we have applied a generalized frequency fluctuation analysis to the Barkhausen signals to detect the various mechanical stresses. Surprisingly, it has been succeeded in clarifying that application of our frequency fluctuation analysis to the Barkhausen signals makes it possible to detect the two kinds of mechanical stress.