PURPOSE: To enable versatile application to varied pipe diameters by holding the entire circumstance of a pipe with a hook provided between an upper and lower chains to retain.

CONSTITUTION: A chain 23 hangs down from a turning device 24. A main body 12 is lowered down on the side of a pipe 11. A chain 16 is sent along a guide 18 and hangs down up to the back side of the pipe. The chain 23 is turned with a driver 24 to get into contact with the pipe 11 and a hook 26 crosses the chain 16. Therefore, as the chain 16 is unwound, a connecting rod 25 is retained with a hook 26 to hold the pipe 11. The main body 12 is drown to the pipe 11 so that a roller 15 tightly contacts the pipe 11 to lock a sprocket 17. An UT sensor 14 is overhung to the pipe 11 until it gets into tight contact with the pipe 11 by a fixed pressing force. As the entire equipment moves along the circumstance of the pipe 11 with the rotation of the roller 15 by the driver, the UT sensor resiprocates along the axis of the weld line part to perform an ultrasonic flaw detection.