An abnormality diagnosis system for diagnosing a presence or absence of an abnormality of a bearing unit for a railway vehicle axle, comprises a sensing/processing portion for outputting a signal generated from the bearing unit as an electric signal, a calculating/processing portion for making an abnormality diagnosis of the bearing unit based on an output of the sensing/processing portion, a result outputting portion for outputting a decision result of the calculating/processing portion, and a controlling/processing portion for feeding back a control signal to a control system of the railway vehicle based on the decision result.