PURPOSE: To prevent the generation of abnormality in shape by setting the driving speed of mandrel bar higher than the speed of a tube in the axial direction of tube on the outlet side of a device for rolling a material in rolling with inclined rolls.

CONSTITUTION: At the same time of starting the advance of the tube in the axial direction of tube, the mandrel bar 7 is advanced in the same direction as the advancing direction of the tube at a prescribed set speed. At this time, the advancing speed of the mandrel bar 7 is set so as to be higher than the advancing speed of the tube 9 on the outlet side of the rolling device 11. Thus, the tube 9 in rolling is forcedly drawn by a frictional force between its inside surface and the outside surface of the mandrel bar 7 to the outlet side of the rolling device with the mandrel bar 7 of which the advancing speed is relatively faster than that of the tube. In such a way, by utilizing a matter that the drawing of the tube 9 in the axial direction of tube is accelerated than that in the peripheral direction in a pass, the generation of projecting parts which are generated on the places where excessive materials are supplied between the rolling rolls 1 in rolling is restrained and the generation of material abnormal in shape can be prevented.