1. An image forming apparatus: image forming means for forming a toner image of a plurality of colors on a recording material; fixing means for heat-fixing the toner image formed on the recording material; detection means for detecting a temperature of said fixing means; actuation means for actuating said image forming means depending on a temperature of said fixing means detected when image formation is started; and change means for changing actuation timing of said image forming means depending on whether a toner image is formed in the plurality of colors or a predetermined single color.