PURPOSE: To more effectively prolong the life of a plug by optimizing the coating quantity of a lubricant on the surface of the plug in accordance with rolling conditions.

CONSTITUTION: As for the coating quantity of the lubricant on the surface of the plug 12 in a skew rolling method of a seamless tube, a ratio X/DB which is the ratio of the traveling distance X of the billet from the point where the billet is brought into contact with a rolling roll 11 to the tip of the plug to the outside diameter DB of the billet or the range of the proper coating quantity by which the life of the plug is improved with respect to piercing efficiency is preliminarily determined, and the coating quantity of the lubricant on the surface of the plug at the time of actual rolling is controlled in the range of the proper coating quantity.