Disclosed is an image reading apparatus in which the band width for reading by one scanning is variable in accordance with the original size, the reading mode, etc. R, G, and B image data of the k-th band is successively read in one-band width to store image data R1, G1, and B1 of pixel coordinates X(n, m). Then, the original is fed so as to cause partial overlapping of the (k+1)-th band with a lower predetermined pixel region of the k-th band, and R, G, and B image data of the (k+1)-th band is read in one-band width to successively store image data R2, G2, and B2 of pixel coordinates X(n, m′). The image data obtained through overlap reading of the k-th band and the (k+1)-th band is averaged to calculate correction image data, which is transferred to a host computer along with along other image data which has not been averaged as read image data. And, it is possible to optimize reading time according to the kind of original, reading mode, etc., without involving a deterioration in image quality.