PURPOSE: To minimize the working time at the time of change in specification between the specifications for two-high and four-high mills.

CONSTITUTION: In a rolling mill which is used both as the two-high mill and four-high mill and which is used for both the specification for two-high mill where a pair of upper and lower work rolls is mounted between roll stands 4 and the specification for four-high mill where respective pairs of upper and lower work rolls W4 and back-up rolls B4 are mounted between roll stands 4, a pair of the same upper and lower driving spindles 20 with which rotational driving force is transmitted to a roll are selectively connected to the work rolls at the time of the specification for two-high mill or the back-up rolls B4 at the time of the specification for four-high mill.