An image forming apparatus whose secondary transfer member is provided with an intermediate transfer belt 6, a bias roll 9 for use in secondarily transferring an unfixed toner image on the intermediate transfer belt onto a recording medium P, and a backup roll which is located in opposition to the bias roll and used for supporting the intermediate transfer belt from the back of the intermediate transfer belt. The intermediate transfer belt is made of belt material of three-layer structure comprising a base made of plastics such as polyimide resin and an electrically-conductive agent, the combination of which has a Young's modulus of 35000 kg/cm.sup.2 or greater, an intermediate layer made of elastic material such as fluororubber, silicone rubber or the like and a surface layer made of material having low surface energy such as fluoroplastics. The thickness of each layer is as follows: the base is 50 .mu.m or thicker; the intermediate layer is three times as thick as a mean tone particle diameter or thicker; and the surface layer is 5 .mu.m or thicker.