An image forming apparatus includes: a plurality of rollers including a drive roller and a follow roller; an endless belt made of an insulation material and looped around the plurality of rollers so that a bridging portion is formed between adjacent rollers and both ends of the bridging portion are supported on the adjacent rollers; a photosensitive drum positioned outside of and facing the outer peripheral surface of the bridging portion; and a transfer roller positioned opposite of the photosensitive drum with the bridging portion interposed therebetween. The inner peripheral surface of the belt is made of a material which has greater tendency to be charged in a polarity that is the same as developer in triboelectric series than the outer peripheral surface of the follow roller as an upstream-side roller.