PURPOSE: To improve the quality of product by displacing the axial center line of a plug bar by a prescribed quantity from the pass line of a mill to the direction of one side of guide shoes located oppositely to each other and setting the chevron-shaped angles of respective main rolls to respectively different angles.

CONSTITUTION: In a skew rolling mill, the axial center of a plug bar 26 for holding a rolling plug 27 is made to coincide with a pass line PL along which a blank pipe passes, and the axes of upper and lower main rolls 21, 22 are set to chevron shaped angles γ1, γ2 which are respectively different with respect to the horizontal plane of pass line PL, and the relation between the angles γ1, γ2 is made to γ1>γ2. Further at need, the axial center of plug bar 26 is previously set by displacing it to the left side with respect to the center line in its longitudinal direction at the pass line PL by a prescribed quantity e.g. about 5W10mm.