To automatize connecting/disconnecting operation between shafts by executing supply and discharge of pressurized oil to a shaft coupling between a spindle shaft and a roll driving shaft with an automatic operation device which is freely attachable and detachable.

A pressurized oil supplying/discharging device 11 in which an oil supply port incorporated with a check valve mechanism is provided and opening means for the check valve mechanism is provided is embedded in a wheel 9, fit in the desired position of an upper spindle shaft 1 and connected to the shaft coupling 5 through piping 21. Simultaneously, an automatic operation device 13 having a mechanism which is automatically connected with and disconnected from this device and, by moving the device forward and backward toward the pressurized oil supplying/discharging device 11, pressurized-oil supplying device 60 and pressurized-oil discharging device 85 are provided. Connection of the spindle shaft 1 with the roll driving shaft 3 is executed by connecting the automatic operation device 13 with the pressurized-oil supplying/discharging device 11 and sealing the pressurized oil from the pressurized-oil supplying device 60 in the shaft coupling 5 and, after that, the automatic operation device 13 is retreated. Disconnection of the shaft coupling is executed by discharging the pressurized oil to the pressurized-oil discharging device 60 with a check valve mechanism releasing means of the pressurized-oil supplying/discharging device 11. A lower spindle shaft 2 has similar structure.