PURPOSE: To prevent the generation of chatter mark by cooling a coupling device with a cooling medium at the time of operation and to facilitate detachment/attachment of the neck part of a work roll by heating with a heating medium at time of changing the roll.

CONSTITUTION: A continuous pierced hole having an intake 12 on one end in the axial direction of the peripheral inside of the recessed part 8a of a yoke 8 of a spindle coupling device 7 and having a takeoff 13 on the other end is arranged in serpentine and a pressure conduit 15 and discharge pipe 16 are respectively connected to the intake 12 and takeoff 13 through a rotary joint 14 which is mounted to the shaft of a reduction gear 5 and a discharge pipe for discharging the heating medium or cooling medium is connected to the takeoff 13. Pipings 19, 22 from a heating medium source 18 and cooling medium source 21 are connected to the pressure conduit 15 through automatic stop valves 17, 20.