An image forming apparatus composes an input image and a form image and generates a composite image, determines whether the image composition processing is designated, and determines whether the maximum amount of applied toner of the form image is not less than a predetermined threshold. Then, the apparatus sets an amount of applied toner of the form image as the amount of applied toner of the composite image if the image composition processing is designated and the maximum amount of applied toner of the form image is not less than the predetermined threshold, and controls, based on a fixing temperature that is determined based on the amount of applied toner, the fixing temperature when performing fixing processing for a printing medium with a toner image that is formed based on the composite image.