PURPOSE: To shorten the time for a roll change by providing a lock pin connecting to a roll in a roll coupling and constituting the same in such a manner that the pin is unlocked by the pressure fluid supplied therein by a remote operation.

CONSTITUTION: The coupling 5 is held on a support 6 in the roll changing stage. The other end of a passage 16 for the pressure fluid in the support 6 is connected via a flexible hose, 17, etc. to a pressure fluid source. The pressure fluid is fed through the passage 16 and annular groove 14 in the support 6 and a passage 13 in the coupling into a cylinder 8 when the pressure fluid is supplied into the coupling by the remote operation, then a ram 9 slides radially outward by overcoming the pressing force of a spring 11. The top end of the ram 9 is disengaged from a roll groove 12 and the connection between the roll and the coupling is released.