PURPOSE: To prolong the life of a mandrel bar by controlling the holding speed of the mandrel bar to respective specific times of inlet rolling speed and outlet rolling speed.

CONSTITUTION: The holding speed of a mandrel bar 2 is controlled during a rolling at 0.25 times or over of an inlet rolling speed and 1.5 times or below of an outlet rolling speed in each roll stand. The reason why the holding speed of the mandrel bar 2 is controlled according to the respective times is that in a retained mandrel mill rolling method, when the holding speed of the mandrel bar is smaller than a certain value, naturally, mandrel bar length to be actually used for the rolling becomes short. In a mandrel mill rolling, only lubricant applied to a part where a material 3 is rolled by a grooved roll 1 and the mandrel bar 2, works on as lubrication during the rolling. To manufacture a product with the satisfactory quality of an inside surface in the mandrel mill rolling, certain lower limit and upper limit exist in the holding speed of the mandrel bar. Consequently, the quality of the inside surface of a hot seamless pipe can be remarkably improved.