To provide an image forming apparatus capable of preventing deformation of a first positioning part and a second positioning part which position a photoreceptor unit in an apparatus body.

In a color printer 1 with a process unit 9 including a pair of left and right side plates composed by combining an inner side plate 32 and an outer side plate 33, both of the inner plates 32 are each provided with an inner notch 38 in the rear edge of the inner plate 32 and with an inner protrusion 37 in the lower edge of the front side of the inner plate 32. The rear end part of the process unit 9 is positioned by bringing the inner notches 38 into contact with a first reference shaft 52 which connects both side walls 51 of a body casing 2, and the front end part of the process unit 9 is positioned by bringing the inner protrusions 37 into contact with a second reference shaft 53 which connects both of the side walls 51.