The distance sensor means and the ultrasonic probe are integrally coupled to each other in such a manner that a preceding scanning line to a current scanning line which is scanned by the ultrasonic probe is scanned by the distance sensor means, and the shape-measurement scanning operation of the distance sensor means and the flaw-detection scanning operation of the ultrasonic probe are performed in parallel with each other. A flaw detection area is divided into plural sub-areas, and plural storing areas are arranged in a mesh form in one-to-one correspondence to the sub-areas, only one shape information of position storing area including the flaw detection area being stored in each of the storing areas. The position and orientation of the ultrasonic probe at each flaw detection point is controlled using the stored shape information.