A duplex image forming apparatus includes a driving unit which has driving rollers and driven rollers to reversely feed the paper printed on the first surface to a duplex printing part or discharge the paper printed on the first and second surfaces, and a separation unit which separates the driven rollers from the driving rollers while the paper printed on the first surface is reversely fed and registered by duplex rollers of the duplex printing part. Accordingly, when the paper is registered by the duplex rollers, because the paper is not caught in the driving rollers and the driven rollers, the paper can be easily registered.