1. An image forming apparatus including a separation mode for permitting a transfer medium, at time of monochrome print, to make contact with only a monochromatic image forming unit and separating the transfer medium from a plurality of remaining image forming units and a contact mode for permitting the transfer medium to make contact with all the plurality of image forming units and enabling the modes to be switched, comprising: judging means for judging, on the basis of image information, whether an image to be printed is a monochromatic image or a full color image; operation mode deciding means for deciding which is used to print the image, the contact mode or the separation mode; and printing means for printing the image in the decided mode, wherein: the operation mode deciding means, at the beginning of a job, decides the separation mode for the monochromatic image and the contact mode for the full color image and after a predetermined condition is satisfied on the basis of previous result information of the job, decides the contact mode for both monochromatic images and full color images.