An image reading apparatus includes an image reader, operable to read an image corresponding to an original and a back pad, the original being placed on the back pad so that outside of the original contains an area extending in overall width of the back pad; a first data generator, operable to generate first image data based on the image; a second data generator, operable to generate second image data based on a part of the image corresponding to the area; a first processor, operable to compare the first image data with the second image data so as to generate first edge information; and a detector, operable to detect an edge of the original based on the first edge information.