PURPOSE: To execute finishing pass downstream from a cooling region by separating a finishing train from a rolling line and replacing the finishing train with intermediate trains when rolling a bar steel with a larger finish cross-section than a smallest possible finish cross-section.

CONSTITUTION: Roll stands arranged on a rolling line 6 are constituted of a front train 1, intermediate trains 2, 3 and a finishing rolling train 4; the intermediate trains 2, 3 are composed of groups of stands - a group 12, 13 and 14 and another group 15, 16 and 17 - each equipped with a pair of a vertical roll and horizontal roll, forming one unit including a driving source. In order to make the unit work at a position 22 for placing the stands, all the stand groups 12-17 to be transferred are installed downstream from a cooling segment 9. When rolling a bar steel with a larger finish cross-section than a smallest plossible finish cross-section, the finishing train 4 is separated from the rolling line 6 and is replaced with the roll stands 12-17 of the intermediate trains 2, 3 adjusted for rolling a bar steel with a larger finish cross-section.