1. An image merging and displaying apparatus for forming an image to be displayed on a display, comprising: a document editing device configured to edit a document by generating document image data; a document image data obtaining device configured to obtain said document image data from said document editing device; a sheet image data generating device configured to generate sheet image data that constitutes a sheet image having a prescribed size in accordance with said document image; an image data merging device configured to merge said document image data with said sheet image data; and a reducing device configured to reduce an image constituted by the merged image data at a prescribed reduction rate to form said image to be displayed on said display.