PURPOSE: To make the thickness in the transverse direction of a plate uniform by providing two pieces of moving housings having rolling down means between stationary housings freely movably.

CONSTITUTION: Two pieces of moving housings 10, 11 are installed between stationary housings 1 and 2 installed on a driving side and a working side so as to be made movable. Each cylinder 21 for moving the housing is driven according to the width of a rolled material 9 and the housings 10, 11 are moved under the guide of upper and lower guide devices 12, 13. A hydraulic drawing down cylinder 28 is driven in the stage of starting rolling to roll down upper and lower backup rolls 7, 7' with upper and lower backup supporting rolls 25, 25'. The material is rolled to the uniform thickness in the transverse direction by the above-mentioned device.