In an image forming apparatus having a fixing unit for fixing a toner image on a printing medium, it is necessary to control a fixing temperature with high precision according to the content of an image. An image forming apparatus of the present invention includes: an input unit configured to input image data; and a controlling unit configured to control the fixing temperature of the fixing unit based on a size of a continuous region of pixels whose pixel values are equal to or larger than a predetermined pixel value in the image data.