In an image input apparatus having an image sensor that is composed of plural chips, the stepwise difference in density on a chip boundary is made inconspicuous by a limited amount of compensation memory. The image input apparatus obtains the stepwise differences in density between pixels that are positioned in adjacent places to adjoining chips of the image sensor and for plural lines, averages the differences, reads an image, and displays the same on a screen after compensating for the stepwise difference in density between the chips for each line by using the average value.