An image reading apparatus which can eliminate a difference of the MTF occurring due to the matching of the positions of the pixels and can perform an accurate color discrimination and can obtain a high image quantity. An image on an original is read through color separation filters of a plurality of colors. By executing position correction arithmetic operations with respect to all of the color pixels which have been read, the pixel positions are corrected without a deviation, thereby setting the MTF of each color pixel to the same level. In the position correction arithmetic operations, by setting a plurality of virtual pixels with respect to each color every pixel on boundaries of different color pixels and by executing the interpolation arithmetic operations, not only the positions can be corrected but also the resolution can be improved.