A fixing device includes a primary heat generator and a secondary heat generator to heat an endless belt and a temperature detector, disposed opposite the secondary heat generator, to detect a temperature of the endless belt. The secondary heat generator includes an inboard edge and an outboard edge disposed outboard from the inboard edge in an axial direction of the endless belt. The secondary heat generator has an inboard length defined between a center of a detection span of the temperature detector and the inboard edge in the axial direction of the endless belt. The secondary heat generator further has an outboard length defined between the center of the detection span of the temperature detector and the outboard edge in the axial direction of the endless belt. The secondary heat generator defines a ratio of the outboard length to the inboard length that is greater than 7/3.