A reading unit, which reads images, reads an image of a predetermined pattern that includes a plurality of marks and is printed on a printing medium by executing scanning relative to the printing medium. Image data acquired by this reading is acquired. Reading adjustment values are specified in accordance with displacement amounts of a plurality of regions with respect to ideal positions. The plurality of regions are formed based on the plurality of patterns included in the acquired image data. Reading processing of a reading mechanism is corrected in accordance with the specified reading adjustment values.