PURPOSE: To provide a device for contracting/expanding of a diameter of a can having simpler structure and lower cost than the one provided currently on a manufacturing line.

CONSTITUTION: The device is provided with a diameter contracting device 1 for applying the drawing work at multi-steps to the opening end of a can C successively, a diameter expanding device 3 for applying the flanging work to the opening end of the can C discharged from the diameter contracting device 1 and a carrier passage 2 provided between the diameter contracting device 1 and the diameter expanding device 3. In the diameter contracting device 1, plural diameter contracting dies are arranged along the carrying direction of the can C, and by advancing the diameter contracting dies at the same time, the opening end of the can C is made to gradually contract the diameter. In the diameter expanding device 3, by advancing the diameter expanding die while linking with the carrying movement of the can C, the diameter of the opening end of the can C is expanded.