PURPOSE: To incorporate side guides keeping sufficient strength without interfering with peripheral equipments by providing a shift mechanism to move the side guides in the width direction of a pass line between slide bases and the side guides.

CONSTITUTION: When an electric motor 8a is driven each of screw axes 2a-3b rotates, slide blocks 4, 5 slide on the sliding surfaces of the slide bases 2, 3 and move in the direction orthgonal to the pass line. Consequently, the side guides 6, 7 integrated with these slide blocks 4, 5, move and can adjust a distance between the both. Since the side guides 6, 7 are driven by a shift mechanism installed in their lower part, the upper sides of the side guides 6, 7 are left as an open space. Therefore, the shift mechanism does not interfere with the overguide arranged on the inlet side of a rolling mill.