1. An image forming apparatus performing a monochrome print mode and a color print mode and having a plurality of system speeds, comprising: a first identification section for identifying whether a print target page in a print target document is color or monochrome and its page attribute; a second identification section for identifying a system speed during printing of an immediately preceding page of the print target page; a third identification section for identifying a presence of a subsequent page of the print target page and its page attribute; and a system speed determination section for selecting a print mode in conformity to a monochrome/color discrimination result based on an identification result in the first identification section and determining a system speed of the print target page based on the page attribute identified by the first identification section and identification results in the second and third identification sections.