An image forming apparatus including: a plurality of image data acquisition units for respectively acquiring one or more page(s) of image data; a color or monochrome determining unit for determining whether each of the acquired pages is in color or in monochrome; an image forming unit for performing image formation of each page switchably using a monochrome-only image forming function for a monochrome page or a color and monochrome image forming function for a color page and a monochrome page; an image data switching unit for sequentially selecting and arranging the acquired pages of image data one by one so that the image formation of each page is performed in the order of selection; a function selecting unit for selecting either one of the monochrome-only and color and monochrome image forming functions for each of the arranged pages on the basis of the determination result made by the color or monochrome determining unit; and a control unit for controlling the image forming unit so that image formation of each page is performed using the selected image forming function.