To provide a method and an apparatus for exchanging an on-the-fly form plate in an ordinary printing unit which does not require transfer of the whole of a printing carriage.

A first printing unit compartment for printing on one side of a web 120, and a second printing unit compartment for printing on the other side of the web 120 are provided. The second printing unit compartment has a blanket cylinder 250, a plate cylinder 260, and a nip roller 300 for adding a pressure to the plate cylinder 260 while a form plate on the plate cylinder 260 is exchanged.