To provide a small-sized device for driving the pressure side of a side roll with which large torque is transmitted.

This device has a screw-down rod 50 in the tip part of which a thread part 49 which is screwed down in the outside part 51 of a yoke 20 of a side roll 14 is formed and in the intermediate part of which, collars 47, 48 for receiving thrust force are provided, 1st and 2nd one-way clutches 58, 59 on which tooth parts 55, 54 for transmitting rotational driving force in the opposite direction are oppositely provided on the base side, power transmitting member 30a which is mounted on the screw-down rod 50 and rotated, with which rotational power is transmitted by engaging to the tooth parts 55, 54 of either of the 1st and 2nd one-way clutches and on a part of which a driving arm 30 which is outwards projected is provided, driving cylinder 31 which is connected to the driving arm 30 and with which the reciprocating turn of the power transmitting member 30a is executed and clutch switching means 34.