According to one embodiment, an abnormality diagnostic device includes processing circuitry. The processing circuitry learns, based on a model generated from sensor data of a diagnostic object in a railroad vehicle, a data selection condition for selecting the sensor data utilized to diagnose the diagnostic object. The processing circuitry diagnoses abnormality of the diagnostic object based on the sensor data satisfying the data selection condition and a diagnostic model representing a relation between the sensor data and the abnormality of the diagnostic object.