An image forming apparatus includes image forming means for forming an image on a sheet; fixing means for fixing an image formed on a sheet; detecting means for detecting a temperature of the fixing means; and controlling means for controlling an image formation start timing in accordance with an output of the detecting means, wherein in an operation of continuously forming images on a plurality of predetermined sheets, when a number of image formations is not less than a predetermined number, start of the image formation is delayed until a temperature of the fixing means rises up to a first temperature, and when the number of image formations is less than the predetermined number, the image formation is started when the temperature of the fixing means rises up to a second temperature which is lower than the first temperature.