PURPOSE: To prevent flaw on the inside and outside faces, angularity and end clogging and to execute high-accuracy rolling by confining the wall thickness/outside diameter ratio of tube stock and the shapes of inclined rolls and plug and setting a draft of wall thickness corresponding to the diameter reduction rate of outside diameter.

CONSTITUTION: In skew rolling that the inside face of a bar for tube is controlled by screwing moving the bar H for tube with three inclined rolls 1 which are arranged around the pass line of the bar H for tube and inserting the plug 2 with a rolling part 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 acompanying with diameter reduction is executed to the bar H for tube. In the conditional formulas, t0 is a wall thickness dimension on the inlet side of the bar for tube, d0 is an outside diameter dimension on the inlet side of the bar for tube, t1 is a wall thickness dimension on the outlet side of the bar for tube, d1 is an outside diameter dimension on the outlet side of the bar for tube, Rd is the diameter reduction rate of outside diameter: Rd=(d0-d1)/d1×100, Rt is the draft of wall thickness: Rt:(t0-t1)/t9×100, D is the gorge diameter 11 of the inclined roll1, β is the inclined angle of the inclined roll 1, θ1 is the inlet face angle 12 of the inclined roll 1, θ2 is the outlet face angle 13 of the inclined roll 1, and θ is the face angle of the rolling part 2b of plug.