PURPOSE: To prevent the generation of the surface flaw of tube due to grain boundary oxidation when heating a billet by preheating the billet on the preceding stage of heating the billet and making the billet into a tube and applying antioxidants on the whole of the surface of a preheated billet.

CONSTITUTION: The billet which consists of an austenitic stainless steel is cut and transported with a crane to store temporarily. Further, after it is rolled on a skid which is transported with the crane and transported with a conveyer to charge into a heating furnace, it is preheated in a preheating furnace or the like which is on-line installed. Then, the preheated billet 1 is applied with antioxidants on the whole of its surface with an automatic spraying device 12 which is provided on a billet transporting truck 11. That is, the billet 1, in a preheated state, is transported just under a manipulator 14 to charge into the heating furnace, while it is revolved on the turning rollers 13 of the billet transporting truck 11 and automatically sprayed with antioxidants with the automatic spraying device 12.