A duplex image forming apparatus including a main body, a recording medium receiving unit disposed on one side of the main body to receive at least first and second recording media, a recording medium supplying unit to feed the first recording medium to a recording medium supplying path, an image forming unit to form an image on a first side of the fed first recording medium, an exiting and reversing unit to discharge the first recording medium formed with the image on the first side from the main body through a direct exiting path in an exiting mode, or to reverse a feeding direction of the first recording medium in a reversing mode, and a duplex feeding unit to resupply the image forming unit with the first recording medium, a rear end of the first recording medium and a front end of the second recording medium being overlapped, to feed the overlapped first and second recording media along the duplex feeding path, and to separate the first recording medium and the second recording medium on the duplex feeding path after a predetermined time.