When image forming is to be successively performed on recording sheets having different sizes, an image forming apparatus suitably executes adjustment processing on a fixing apparatus or the like used in the image forming, and maintains image quality as well as suppresses a drop in productivity. To accomplish this, the image forming apparatus specifies the size of a printing material onto which an image is to be performed, and with use of the specified printing material size and the size of printing materials on which images have been formed immediately previously, determines whether it is necessary to execute adjustment processing for maintaining image quality. Specifically, adjustment processing is executed only if the size of the printing material on which an image is to be formed is greater than the size of the printing materials on which images were formed immediately previously.