PURPOSE: To reduce the size of a small-diameter work roll and to make possible high-draft rolling by providing pressure grasping devices which grasp the small- diameter work roll under the pressure.

CONSTITUTION: The pressure grasping devices 9, 10 which grasp the small- diameter work roll 31 under the pressure are provided and the roll 31 is grasped under the pressure by reinforcing rolls 5, 6 from the front and rear directions. Large-diameter work rolls 1, 3 are driven in the same direction and since the roll 31 is not-driven, the roll is limited from the limitation in torsional rigidity. Since said roll is grasped and held under the pressure by the rolls 5, 6, the roll is released from the limitation in bending rigidity. The diameter is thus considerably reduced and the high-draft rolling is made possible.