A fixing device for fixing a toner image formed on a recording medium includes an endless belt passed over a plurality of rollers. A press roller is pressed against a portion of the belt passed over a fix roller, which is one of the plurality of rollers. A heat source applies heat to the toner image carried on the recording medium being conveyed via a nip where the belt and press roller are pressed against each other. The nip has a width greater than 25.degree. inclusive in terms of a circumferential angle as seen from the axis of the fix roller. The fixing device prevents a recording medium from wrapping around the belt and broadens a parting temperature range.