PURPOSE: To make it possible to remotely detect the flaw position of the core spray piping in an atomic reactor, by moving a flaw detection head between frames attached to both ends of piping to be inspected.

CONSTITUTION: A flaw detection apparatus is fallen toward core spray piping 2 from the upper working floor of an atomic reactor in a suspended state and a flaw detection head 11 is set to the outer peripheral surface of the piping. Next, the air cylinder of a clamp mechanism 7 is operated to hold the piping 2 between left and right frames 13a, 13b and the flaw detection head 11 is subsequently driven to start flaw detection work. In order to drive the flaw detection head 11, a motor 19 used in the movement in a revolving direction and a motor 24 used in the movement in an axial direction are started. By this method, the flaw ditection in axial and revolving directions can be performed. When the inspection between the left and right frames was completed, the flaw detection head 11 is fixed by an air cylinder 25 and the clamp mechanism 27 attached to the left and right frames are opened and the motor 24 used in the movement in the axial direction is started to move the piping fixing position of the left and right frames to perform the flaw detection of a new region.