[en] A laser ultrasonic inspection system is a non-contact inspection device which generates and measures ultrasounds by using a laser beam. A laser ultrasonic inspection system provides a high measurement resolution because the ultrasonic signal generated by a pulse laser beam has a wide-band spectrum and the ultrasonic signal is measured from a focused small spot of a measuring laser beam. In this paper, we have studied a discrimination technique for a crack by a spectrum analysis of multi laser ultrasonic signals. We experimentally confirmed that the defect information can be extracted through observing the frequency of the attenuation variation of coefficients