A device for printing a document, such as an HTML document, in which data to be incorporated into an output image can be described in the form of reference to an outside source, the device being capable of smooth printing a large document using a small memory. A document structural information manager creates document structural information which describes a structure of document elements, based on a result of analysis on an HTML document carried out by a document analyzer. During asynchronous downloading of substantial data of each document element, should work memory shortage occur, a memory manager unloads substantial data of a document element with a latter order at which to be incorporated into an output among those in the work memory, and saves the unloaded substantial data in an HDD. Thereafter, when data becomes no longer necessary as a result of being printed, the memory manager deletes the data from the work memory and reloads data saved in the HDD back to the work memory.