Fixing unit including heat roller with tubular heater and fitting surface

A fixing unit comprising,

• a casing;
• a heat roller that is rotatably supported and that supplies heat for fixing;
• and
• first and second tubular heaters that are disposed in parallel in the heat roller along an axis thereof, the first and second tubular heaters each comprising a lead wire having a protruding end portion protruding outwardly from an axial end portion thereof and a flat terminal having one face thereof connected and fixed to the protruding end portion,
• wherein a first fitting surface for fixing the flat terminal of the first tubular heater and a second fitting surface for fixing the flat terminal of the second tubular heater are formed in the casing,
• the first fitting surface is arranged to be flat at least in an area in which the protruding end portion of the first tubular heater is disposed,
• the second fitting surface is arranged to be flat in an area excluding an area in which the protruding end portion of the second tubular heater is disposed and is provided with a clearance for storing the protruding end potion of the second tubular heater,
• the flat terminal of the first tubular heater is fixed to the first fitting surface with a face opposite to said one face of the first tubular heater facing the first fitting surface,
• the flat terminal of the second tubular heater is fixed to the second fitting surface with said one face of the second tubular heater facing the second fitting surface, and the first fitting surface has a step difference relative to the second fitting surface.