An image forming device, an image forming method, and a program intended to print out multiple documents of different sizes collectively in one output sheet with a margin upon adjustment of the magnification of the documents to an appropriate size. The image forming device used for combined printing is capable of printing image data obtained from multiple documents into one output sheet which includes a margin generating section for generating a margin area upon the output sheet, a document arranging section that arranges the multiple documents in a document depicting area without the margin area in the output sheet with respect to one corner of the document depicting area as a reference for the purpose of minimizing the generation of blanks, and a magnification processing section that adjusts the magnification of the multiple documents in order to make them fit into the document depicting area.