PURPOSE: To prevent selective oxidation when heating a billet and in its turn to prevent the generation of the pressed flaw of oxidized scale on the surface of tube by rolling the billet as it is without repairing when the number of surface flaw of billet that the degree of surface defect of billet isn't less than the referrence defect degree is less than the critical number of flaw.

CONSTITUTION: A billet which consists of an austenic stainless steel and to which billet inspection is executed after it is rolled with a billet mill is treated with its defect by either of a following (1) or (2) in accordance with the number (n) of surface flaw of billet that the ratio of the depth (t) of surface flaw of billet to the diameter D of billet, i.e., the surface flaw degree t/D is more than the reference defect degree (a)=0.5% is less than (na)=10/m or not. (1) When (na) is less than 10/m, the surface flaw of billet is repaired after it is heated as with the skin and made into the tube, and, further, the flaw due to heating/ tube making is repaired. (2) When (na) is not less than 10/ m, the billet is heated and made into the tube after the skin is peeled and, after that, the flaw due to heating/tube making is repaired.