PURPOSE: To automatically execute an ultrasonic flaw detection to not only a straight part of a pipe but also a bent part, by constituting so that a guide rail for bearing an ultrasonic vibrator is positioned on the same plane as a plane including a weld part to be inspected, and a distance between the guide rail and the weld part is always kept constant even if a pipe is bent.

CONSTITUTION: On both sides of a guide rail 101, a setting arm is project- molded, a setting bolt 103 is screwed to the tip part of this setting arm 102, the guide rail 101 is set and fixed by each setting bolt 103, and a moving base 106 is moved along this guide rail 101. An ultrasnoic flaw detection is executed by moving an ultrasonic probe 107 provided on this moving base 106, along the circumferential surface of a pipe 104. As a result, the guide rail 101 can be positioned on the same plane as a plane including a part to be inspected, for instance, a weld part 105, therefore, a distance between the guide rail 101 and the weld part 105 is always kept constant even if a pipe is bent, and the ultrasonic probe can be moved along the outside circumference of the pipe 105 at all times.