1. An image forming device for dividing a continuous document into pages for image formation, comprising: page dividing means provided with a plurality of page dividing algorithms, for dividing the document into a plurality of pages; algorithm designation means for designating by a user one page dividing algorithm to be used among the plurality of page dividing algorithms; and control means for controlling the page dividing means to divide the document into pages according to the user-designated page dividing algorithm by the algorithm designation means.