The laser ultrasonic method is nondestructive evaluation method that uses short, Q-switched,pulse laser to generate and CW(continuous wave) laser to detect ultrasonic waves. It has an advantage that the sensors are no need to be contact with the specimen surface. And it has gotten a lot of attention recently such a new non-destructive inspection. In this paper, laser-generated ultrasonic wave in a carbon steel sheet is received by piezoelective transduser, and we measure board thickness from the experimental results.