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As diagnosis methods for bearings, well-known are those which use acceleration sensors. But, the diagnosis method cannot be applied when the bearing is invisible. For such a case, the diagnosis can be achieved by measuring the vibration of the shaft. Although an eddy current sensor (displacement sensor) is applicable to the sensing of the vibration, the sensing from a distance is impossible. With an application to the diagnosis of the bearing in sump pumps in mind, the paper proposes a signal propagation model based diagnosis method of the shaft vibration using an ultrasonic sensor which is attached on the casing surface. The effectiveness of the method is finally demonstrated with simulation data.