PURPOSE: To reduce the roll cost by converting cutting both the groove-bottom part of roll and edge part of each grooved roll of stands into an intermediate roll for relevant stand and the stand of the preceding stage and using that roll for these stands.

CONSTITUTION: Both the groove-bottom part and edge part of each grooved roll 1 of the stands are converting cut into the intermediate roll for relevant stand and the stand of the preceding stage and that roll is used for these stands. Consequently, the roll is converting cut about twice into the intermediate roll until the roll is converting cut into the dimensions of the grooved roll for these stands, usable for these stands and the number of rolling pass of each roll until the roll is converting cut into the dimensions of the grooved roll for the preceding stand is remarkably increased and the roll consumption unit is improved. Furthermore, the effect on the seamless tube of a product by using the roll which is converting cut into the intermediate roll for these stands is not a problem especially in all the dimension of outside diameter, degree of ellipse and ellipticity.