An image forming apparatus comprises a scaling correction circuit that corrects scaling in a sub-scanning direction of image data according to scaling data, a screen processing circuit that, of image data whose scaling in the sub-scanning direction has been corrected by the scaling correction circuit, performs screen processing on image data included in a screen area; and an image forming unit that forms an image based on the image data that has been processed by the screen processing circuit. The scaling correction circuit changes the scaling in the sub-scanning direction such that a pixel arrangement of the screen area after the scaling is changed becomes a pixel arrangement of image data before the scaling was changed.