PURPOSE: To freely set a tube length and to execute high-efficiency and high-quality rolling by specifying the diameter reduction rate of tube when rolling and the shapes of an inclined roll, guide member for bar for tube, plug, etc.

CONSTITUTION: In skew rolling that the inside face of the bar for tube is controlled by screwing moving the bar H for tube with inclined rolls 1, 1 which are arranged around the pass line of the bar H for tube while restraining the bulge of the bar H for tube with the guide members 3 which are arranged around the pass line of the bar H for tube, floatably inserting/supporting the plug 2 with a rolling part 2b of which the outside diameter is gradually reduced in the rolling direction into the bar H for tube, conditional formulas are satisfied and elongating rolling accompanying with diameter reduction is executed to the bar H for tube. In the formulas, d1 is the outside diameter dimension on the outlet side of the bar for tube, d0 is the outside diameter dimension on the inlet side of the bar for tube, β is the inclined angle of the inclined roll 1, pθ1 is the face angle of the rolling part 2b of plug, Rq1 is the inlet face angle 12 of inclined roll, G is the opening degree of the guide member 3 for bar for tube, Rg is the opening degree of the inclined roll 1, Rθ2 is the outlet face angle of inclined roll, Gθ1 is the inlet face angle of the guide member 3 for bar for tube, Gθ2 is the outlet face angle of the guide member 3, and PD is the maximum diameter of plug.