In an image forming apparatus, a toner image formed on an intermediate transfer belt is transferred to a transfer sheet by a transfer electric field generated between a secondary transfer roller and a driving roller. A guide surface of a pre-transfer guide and a flat portion of the intermediate transfer belt form an angle of no less than 13.degree. and no greater than 17.degree., and a distance from a tip of the guide surface and the flat portion is no less than 1.0 mm and no greater than 3.0 mm.