PURPOSE: To provide a fixing device capable of highly accurately controlling temperature while precisely detecting the temperature even in the case of causing paper winding or paper powder without scratching the surface of the heating roll of a paper passing area.

CONSTITUTION: In this fixing device of an image forming device fixing an image on a copying paper by the heating roll 1 having a heater inside and a pressure roll, a contact type temperature sensors abutting on the surface of the roll 1 are arranged on both sides of the roll 1 being outside the paper passing area of the maximum-sized copying paper. Besides, one of both temperature sensors provided on the outside of a paper passing reference area where the copying paper is always passed is used as the temperature sensor for controlling lower limit temperature STS1 and the other temperature sensor is used as the sensor for controlling upper limit temperature STS2. Also, the fixing device is provided with an electric power control means 4 controlling the surface temperature of the roll 1 based on signals detected by both temperature sensors.