An image forming apparatus including a side cover rotatably installed to open and close an opening provided at a body thereof while rotating, a first transfer unit to which a visible image of photoconductors of developing units is transferred, and a second transfer unit movably installed at the side cover to transfer the visible image to a printing medium, wherein the second transfer unit is provided at both sides thereof with a plurality of guide protrusions to perform a position restriction, and the body is provided at both sidewalls of inside thereof with a plurality of guide members to support the plurality of guide protrusions such that the second transfer unit is supported against both sidewalls of the inside of the body through the guide protrusion and the guide member, thereby reducing a reaction force applied to the side cover.