An image scanning apparatus determines whether there is an influence of external light from the outside of the image scanning apparatus on scanning; decides a correction value corresponding to each of a plurality of sensors based on received light amounts of at least some of the plurality of sensors; and corrects, using the correction value corresponding to each of the plurality of sensors and decided, data corresponding to a received light amount of each of the plurality of sensors when scanning the original, wherein if it is determined that there is the influence of the external light, the image scanning apparatus decides the correction value corresponding to a first sensor and the correction value corresponding to a second sensor arranged at a position that is readily influenced by the external light based on the received light amount of the first sensor.