An image forming apparatus comprises a developing unit and a developing unit attaching portion that is provided in an apparatus main body. The developing unit and the developing unit attaching portion are provided with an insertion guide. The insertion guide makes the developing unit a state it is inclined from a normal posture so as to be moved on a position departed from a photoreceptor drum during a period from a start of insertion of the developing unit into the developing unit attaching portion until just before completion of the insertion, and makes, during a period from just before completion of the insertion until completion of the insertion, the developing unit turn according to an insertion operation of the developing unit so as to be brought close to the photoreceptor drum, whereby the developing unit is positioned so as to take the normal posture.