When a host computer makes a printer print a document, the driver on the host computer sends character codes of characters that appear for the first time in that document and corresponding character images to the printer in advance, and registers them. After this process, the driver transmits, to the printer, characters in the document to be printed as character codes, and data other than characters as mapped image. The printer maps an image on a page memory, maps characters as images with reference to the registered character codes and character image, and superposes the mapped character images on the image mapped on the page buffer. The printer prints the image on paper. The printer can divide an image into bands, and can map the image in units of bands, in place of pages. With this arrangement, the memory capacity can be reduced, and bands having identical contents or blank bands can be processed as codes.