In an image forming apparatus using a transfer unit of a roller transfer method, the contact between the transfer unit and a photoreceptor drum can easily be canceled. The transfer unit is brought into contact with the photoreceptor drum by supplying an upward pushing force to a supporting member of the transfer unit, and a lever engaging with the supporting member to push down the supporting member is provided to connect with a front cover of the apparatus body. The transfer roller, the pre-transfer roller for feeding a sheet to the photoreceptor drum and driving force transmitting gears provided therebetween are supported by the same member to fix their relative positions so that the driving force is constantly transmitted from the transfer roller to the pre-transfer roller.