PURPOSE: To prevent the bend and inclination of the flange during the straightening work, by making the width of the latter half rollers to be larger than that of the first half rollers to the amount of stretch in the height of H-beam generated at the straightening work.

CONSTITUTION: The H-beam 2 is passed through the straightening rollers 11W19 being zigzag arranged in the straightening machine 1; hereby, the shape of H-beam 2 is straightened. Hereupon, since the rolling reduction given to the H-beam 2 by rollers 12W15 is the maximum, the set width (l) of rollers is changed so as to enlarge at rollers 15W19 on the exit side, to the amount of stretch in the height L of H-beam. Though this stretch in the height L differs with the size of H-beam, usually it is about 0.5W2.5mm, by which almost constant clearance can be secured over entire range from the entry to the exit of the straightening machine.