In a color image forming apparatus, a color mode is switched from a full color mode to a single color mode as follows. When the length of an image of a last page in the full color mode is less than the distance from a first-transferring position of a most downstream image forming station to a second-transferring position, if the time interval from arrival of the trailing end of an image of a page immediately previous to the last page at the second-transferring position to arrival of the leading end of the image of the last page at the second-transferring position is longer than the time needed to separate color image forming stations from the second image carrying medium, then the separating operation is started when the trail end of the image of the page immediately previous to the last page in the full color mode reaches the second-transferring position.