An image reading apparatus having an auto document feeder includes a simplex path for simplex reading, a duplex path which is distinguishable from the simplex path and conveys a plurality of sheets of paper at different positions in a duplex reading mode, a path selecting element, and a flipping element which allows a second side of paper to be read first. Accordingly, in the duplex reading mode, a separation distance between sheets of paper is reduced, a returning path is reduced, the second side of paper is first read, and the paper is collated and then discharged after both sides of paper are read, thereby significantly improving duplex reading efficiency.