PURPOSE: To set plate cylinders of different diameter replaceably to carry out the printing of different print sizes by one printer and perform the replacement work quickly, securely and with good workability.

CONSTITUTION: A main machine unit 11 with an ink feed device, a wetting device and a driving shaft is provided and a print cylinder unit 15 comprising print cylinders such as plate cylinders and blanket cylinders installed thereon and mounted removably on a print cylinder unit mounting section on the main machine unit 11 is also provided. A guide rail 67 extending in the mounting and demounting direction of the print cylinder unit 15 is set on a print cylinder unit mounting section, while a wheel 113 engaged with the guide rail 67 and rolling on the guide rail 67 is provided on the print cylinder unit 15.