PURPOSE: To achieve a smaller size of a flaw detector, by a method wherein a rotary orbit is provided on a stationary orbit on the circumference of a cylindrical object, a flaw detection body moving unit mounted thereon and a driving source set outside the rotary orbit for the rotary orbit and a probe moving mechanism.

CONSTITUTION: A stationary orbit 8 is mounted on the circumference of a cylindrical object 1 to be inspected like a piping. A rotary orbit 9 turns on the stationary orbit. A probe moving screw 10 mounted on a flaw detection body moving unit 11 moves a probe coaxially with respect to the cylindrical object 11. The flaw detection body moving unit 11 rotates circumferentially with respect to the cylindrical object 1 together with the rotary orbit 9 driven by a driving source 12. The distance of the unit 11 moved in the circumferencewise direction of the cylindrical object 1 is indexed with deceleration/indexing mechanism 15 by the rotation of a pinion 14 following the unit 11. The unit 11 moves at a fixed distance in the circumferencewise direction of the cylindrical object I and a probe moving screw 10 is turned to move the probe at a fixed distance axially with respect to the cylindrical object 1.