To prevent adhesion of dirt onto the light-receiving window surface, and to perform accurate temperature detection, by reducing unnecessary infrared rays other than from the view angle.

This thermal fixing device has a constitution, wherein a heating roller 2 having a heater inside and a pressure roller 4 are in pressure-contact state, and also has a constitution wherein a recording paper 11 is moved in the arrow direction between the heating roller 2 and the pressure roller 4. For the surface temperature of the heating roller 2, the infrared rays, radiated from the heating roller 2, are detected by a temperature detection device 53, constituted to include a noncontact temperature sensor 1. The temperature detecting device 53 is constituted of a sensor holder 21, a sensor module 51, and a sensor presser member 26, and the sensor holder 21 is formed integrally from a heat-resistant resin or the like, having low thermal conductivity, to thereby suppress the temperature rise to be low. The sensor holder 21 is constituted of a shell part 22, and a cylindrical eaves part 23, and the eaves part 23 is faced to a fixing roller 2 which is an object to be detected.