PURPOSE: To extract the characteristics of the reflected wave motions caused by the differences of the shapes of reflecting sources in a method for detecting the characteristics of the wave motions such as a nondestructive inspection method.

CONSTITUTION: In this method for extracting the characteristics of wave motions, the wave motion is cast into a body. The incident wave motion is reflected from a reflecting source, which is present in the body. The reflected wave motion is detected at the surface of the body. Only the wave motion, which is reflected from the reflecting source, is taken out of the detected wave motions. The frequency of the taken-out wave motion is decomposed. The characteristic amount of the frequency of the wave motion, which is decomposed into each frequency, is computed. The characteristics based on the difference of the shape of the reflecting source with respect to the computed characteristic amount of frequency of the wave motion is extracted.