PURPOSE: To improve additionally not only the size of a roll finished pipe but also the sectional shape thereof by enabling theoretical setting of the number of revolutions of each stand according to the actually measured tension between stands and enabling control of the pattern for distribution tension to each of the stands.

CONSTITUTION: The initial pattern for the reference number of revolutions is calculated by the predicted tension coefft. ZAi from the outside diameter and wall thickness of a base pipe and the outside diameter and wall thickness of the roll finished pipe 5. The number of revolutions of the rolls is set for each of the roll stands 7 and the base pipe is subjected to stretch reducing. The tension Ti between the stands 7 during rolling is actually measured by a tension measuring device 21 via a load detector 12 and is inputted to a calculator 22 for control with a hot stretch reducer 4. The calculator 22 calculates the coefft. Zi of the actually measured tension of each stand 7 according to the actually measured tension Ti and corrects the pattern for the number of revolutions of the rolls by learning according to the deviation between both coeffts. ZAi and Zi. The control of the number of revolutions of the rolls with high accuracy is thus made possible.