1. An image forming apparatus in which image making unit provided with developing units having at least developing devices and carrier units having image carriers for toner images to be formed thereon by the developing devices and supports for supporting the image carriers are disposed at least two along a moving direction of a transfer material, the developing units and the carrier units of the image making unit are individually independently attachably and detachably mounted to an image forming apparatus body, and the toner images formed on the image carriers of the image making unit are transferred to the transfer material, wherein a common guide member adapted, when a carrier unit of one image making unit of two image making unit neighboring each other and a developing unit of the other image making unit are attached to or detached from the image forming apparatus body, for guiding the carrier unit and the developing unit respectively is provided.