To provide a lithographic printer capable of printing with good damage resistance, plate wear resistance and image reproducibility by forming an image pattern by a computer-to-plate technology and a simple water developing operation by automatically mounting an original plate for a lithographic printing plate in the printer or automatically platemaking a printing plate without necessity of a water developing treatment.

The lithographic printer comprises a plate cylinder 2 having a mechanism for containing a used image-forming material 4 therein after completion by supplying an image-forming material 5 for a lithographic printing plate from an interior, mounting the material 5 on an outer periphery, and forming and printing the image. In this case, the image-forming material contains a polymer compound having a functional group changing in hydrophilic and hydrophobic properties according to a heat.