A fixing device is provided including a plurality of supporters, an endless belt movably supported by the supporters in a main direction, a heat source which heats the endless belt, and a pressing element which presses on the endless belt. Two bridging portions of the belt extend between the supporters, one bridging portion is tensed, the other bridging portion is tense-free. A fixing nip is formed by contacting the pressing element with an outer surface of the tensed bridging portion. The fixing device further includes a heat source which heats a rounding portion of the belt that is wound around a supporter on an upstream side and a cleaning mechanism which cleans a surface of the rounding portion.