PURPOSE: To improve the productivity of a rolled product by shortening the time required for a change of plural rolls of a rolling mill.

CONSTITUTION: At the time of detaining and detaching a drive shaft and a hub of a coupling 7 for rotating a roll of a rolling mill 8, the time required for detaining and detaching said drive shaft and coupling 7 can be shortened in a change work of the roll by executing stop control of a motor 5 for driving a multishaft speed reducer 6, therefore, in connection with the improvement of an operation rate of the rolling mill 8, productivity of a rolled product can be enhanced.