PURPOSE: To expand the adequate set ranges of a roll gap and plug position to obviate the generation of defects by determining one rolling roll as a reference roll and correcting the spacing of the other rolling roll from a rolling pass line in accordance with the shift quantity of the two rolling rolls.

CONSTITUTION: The rolling roll 2A with which the gorge position F1 exists on the rear side of the rolling pass line is determined as the reference roll for setting the gorge E and lead L as to the stock size which is not enough in the number of idle rolling. The spacing of the other rolling roll 2B from the rolling pass line is corrected in accordance with the shift quantity l of the two rolling rolls 2A, 2B. Namely, the gorge E and lead L to obtain the wall thickness (t) of the pipe stock are calculated. The gorge E and lead L are set on the basis of the gorge position F1 of the rolling roll 2A. The spacing of the gorge position F2 of the rolling roll 2B from the rolling pass line can be corrected merely by reducing the gorge E by ΔE1=ltanβ2 from the geometrical relation based on the shift quantity l of the two rolling rolls 2A, 2B.