PURPOSE: To secure a prescribed target length by reducing the variation in length in the final stage of rolling.

CONSTITUTION: The actual length of a base stock which is obtained in the stage just before the final stage of rolling is compared with the intended length and, in the case the actual length is longer than the intended length, that base stock is made into a rolled product longer than the intended length by executing the final rolling under a prescribed thickness tolerance/weight tolerance. Occurrence of shorter product than a prescribed length by cutting the defective part having defective dimension and bending and the like in the end parts of the final rolled product, is reduced, especially, in the case of seamless steel tube, retained amount is reduced and yield is improved.