A planar heat-generating body 42 of a fixing apparatus of the present invention includes (i) a resistive heat-generating body 43a containing small heat-generating bodies electrically connected in parallel and aligned in a direction perpendicular to a direction in which a fixing belt 32 moves and (ii) a PTC element and a corresponding small heat-generating body being provided to be connected in series with a power source 36, the PTC element having a resistance value increasing at a predetermined temperature or higher. The PTC element 37 and the small heat-generating body are provided in an area corresponding to a non-sheet passing area of the fixing belt 32, the non-sheet passing area being an area where a smallest-size sheet does not pass, the smallest-size sheet being smallest among sheets that the fixing apparatus deals with. This allows for prevention of a temperature increase in the non-sheet passing area with a simple arrangement.