PURPOSE: To improve the accuracy of a wall thickness of pipe, by measuring a tension between adjoining stands as well as computing the deviation between the measured tension and a target one and controlling the number of revolutions of a rolling stand of the pipe end so as to make the deviation to be zero.

CONSTITUTION: Each stand of a stretch reducer 7 is driven by a motor 6, and is provided with a tension detecting device 2. The device 2 has shearing type load detectors (load cell) 12, which are incorporated in upper and lower rails 10 and 11 respectively. As the forces acting between a roll stand 13 and the upper and lower rails 10, 11 are respectively transmitted through the detectors 12, the stress acting on the stand 13 in the rolling direction is obtained. An interstand tension is computed based on said stress and each boundary conditions, and the deviation between the computed tension and a target tension is inputted to a computer 4, to control the number of revolutions of a stand of the pipe end. In this way, the accuracy of a wall thickness of pipe is improved.