PURPOSE: To drastically improve the yield of product in the manufacture of a seamless steel tube by an inclining rolling method.

CONSTITUTION: In the stage of design of a billet which is fed to a inclined rolling mill, the equivalents 7 to irregular parts at tube ends on the top and bottom sides after making the tube which are made of a surplus billet 8 are joined to the top and bottom sides of a design billet 6 which the equivalents to irregular parts at the tube ends on the top and bottom sides after making the seamless steel tube are subtracted by welding, pressure welding, or the like and, after that, they are heated, pierced, maked into the tube and the irregular parts at the tube ends and a surplus length part are cut off. Then, the yield of product is drastically improved by effectively utilizing the surplus billet.