The present invention provides a technique that makes it possible to realize highly accurate shading correction regardless of presence of dust or the like in a shading correction plate without preventing a reduction in a size of an apparatus. An image scanning apparatus determines an area where dust is present in a reference area, which is an object of scanning of reference data used for shading correction in the image scanning apparatus, scans the reference data from an area excluding the area where it is determined that dust is present, and performs shading correction on the basis of the reference data scanned from the area excluding the area where it is determined that dust is present.