In an image scanning system which can scan an image in a plurality of scanning modes, and has a memory for storing a correction data file which has correction data for each of the plurality of scan modes, correction data corresponding to a scan mode of a given image scan operation is read out from the memory upon scanning an image, and an image scan is executed using the readout correction data. If correction data corresponding to the scan mode of that image scan operation is not stored in the memory, correction data corresponding to the scan mode is generated, and is stored in the memory.