To enable an abnormal cause to be displayed according to detection accuracy, and to enable two or more samples of the abnormal cause to be displayed with importance when any one of the abnormal causes is not specified.

A characteristic vector is extracted by subjecting an abnormal wave shape of a yarn tension in a draw-false texturing machine to wavelet conversion, and the extracted characteristic vector is treated by a self-organizing map (SOM). The result treated by the SOM is two-dimensionally visualized and displayed on a terminal. The array of the units of the SOM is arranged two-dimensionally in the display. The unit of specifying the abnormal cause is labeled, and the units most adjacent to the extracted characteristic vector are displayed by marking.