A fixing device for thermally fixing an unfixed image formed on a recording sheet by passing the recording sheet through a fixing nip. The fixing device has a heat-generating endless belt that includes: a resistive heat layer that generates heat upon receiving electric current; and a pair of electrode layers each disposed along a different one of widthwise edges of the heat-generating endless belt. The resistive heat layer has (i) reduced thickness portions each along a widthwise edge thereof and (ii) a middle portion between the reduced thickness portions. Each reduced thickness portion is thinner than the middle portion and connected to the middle portion with a wall surface upright in a direction perpendicular to the rotation axis of the heat-generating endless belt to define a stair shape. Each electrode layer is disposed on the resistive heat layer to be in contact with a corresponding one of the wall surfaces.