PURPOSE: To efficiently perform attaching/detaching the coupling of drive shaft by providing a clamping means for fixing the coupling, elevating/lowering means for elevating/lowering an unit for attaching/detaching coupling and clamp operating means for making the clamping means into unclamped state.

CONSTITUTION: A fine adjustment of the height and angle of the couplings 4, 5 is executed by elevating the units 18, 19 for attaching/detaching coupling with the elevating/lowering device 20 in accordance with the height of pass line and angle of inclined rolls 2, 3. Regarding to the position change of drive shafts 10, 11 or the couplings 4, 5, devices 6, 7 for attaching/detaching coupling are made in unclamped state by the action of cylinders 8, 9 for attaching/ detaching coupling which are provided to the devices 6, 7 for attaching/detaching coupling. In this way, the coupling 4, 5 follow the drive shafts 10, 11 and are inclined and the rotation is transmitted.