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; 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 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 identification results in the second and third identification sections, wherein when the second identification section identifies that the system speed during printing of an immediately preceding page is a monochrome system speed, then the third identification section determines whether the subsequent page of the print target page is a monochrome page.