A fixing device for an electrophotographic image forming apparatus is provided with a heat roller configured to heat a toner image formed on a sheet, and a thermistor arranged opposite to a circumferential surface of the heat roller and configured to detect a temperature of the circumferential surface of the heat roller without contacting the heat roller. The thermistor is located at a position above a horizontal plane including a rotational axis of the heat roller and on a downstream side, in a rotational direction of the heat roller, with respect to a vertical plane including the rotational axis of the heat roller, and closer to the vertical plane than the horizontal plane.