PURPOSE: To improve the dimensional accuracy of a steel pipe by attaining the target rolling torque meeting the rolling speed of a reeling mill in order to attain the coincidence of a thickness rolling reduction and a target thickness rolling reduction.

CONSTITUTION: The target thickness rolling reduction is calculated by a control arithmetic unit 6 from the thickness of a pipe stock 1 to be rolled by rolling rolls 2 of the reeling mill and the target thickness after rolling. The target rolling torque for attaining the target thickness rolling reduction is determined by the control arithmetic unit 6 from the actually measured rolling speed of the reeling mill detected by a stock pipe rolling speed detector 7 and the target rolling torque is obtd. by controlling the rolling down position of the rolling rolls 1 and/or the advance position of a plug 3. The coincidence of the thickness after the reeling mill rolling with the target value is attained in this way.