PURPOSE: To greatly reduce the manufacturing manhour for a metallic tube having an inside spiral groove by piercing and rolling a metallic tube of a solid circular section in a hot state through a skew rolling mill in which a plug provided with a spiral groove is arranged and fixed.

CONSTITUTION: The skew angles of rolls 1, 2, 3 and the crossed axis angles between them are set suitably and while they are rotated and driven in the same direction, metallic material 7 of a solid circular section is bit into them and at the same time a plug 4 is penetrated into the central part. The metallic material 7 is charged by the pressure of the rollers 1, 2, 3 in a spiral 4a and moved spirally and makes a metallic tube 8 having a spiral groove. Since the metallic material 7 of a solid circular section is pierced and rolled in a hot state to directly manufacture a metallic tube 8 having an inside spiral groove, manhours can greatly be reduced and the manufacturing cost can be reduced.