A fixing unit includes: a casing; a heat roller that is rotatably supported and that supplies heat for fixing; and a tubular heater disposed in parallel in the heat roller along an axis thereof. The tubular heater includes a lead wire having a protruding end portion protruding outwardly from an axial end portion thereof. In addition, the tubular heater includes a flat terminal having one face thereof connected and fixed to the protruding end portion. Moreover, a fitting surface for fixing the flat terminal is formed in the casing. The fitting surface is arranged to be flat in an area excluding an area in which the protruding end portion is disposed and is provided with a clearance for storing the protruding end portion. Further, the flat terminal is fixed to the fitting surface with the one face of the flat terminal facing the fitting surface.