An image forming apparatus having means for separating a transfer medium bearing member from an image bearing member, which can change fixing speed according to the kinds of the transfer medium employed. As the transfer medium is borne and conveyed to a fixing device by the transfer medium baring member which is separated from the image bearing member, the unfixed toner images are not disturbed by or re-transferred onto the image bearing member and a long conveyed belt is not needed. When the same drive source rotates the transfer medium bearing member and the image bearing member, the apparatus can be further miniaturized.