To solve the problem that a noncontact temperature detector in an easily fouled environment is not properly controlled in temperature because various kinds of dirt adhere to the window member of the infrared-ray receiving window of the detector and the infrared-ray tranmitting state of the member changes even at the same temperature.

In the fixing device of an image forming device, a noncontact temperature sensor 1 having an infrared ray-transmissive window member 7 is contained in a sensor holder 24 and attached to a partition wall 30 through a holder fixing angle 32 and a frame fixing angle 31. The sensor 1 is set up to face part of a heating roller 2 which is an object to be detected through the light receiving window 35 of the sensor holder 24 and the opening 45 of the partition wall 30. On the surface of the window member 7, a coating film 40 of an organic fluorine compound, for example, a fluorine-based resin or fluorine-based oil is formed. The vapor of Si oil or wax or floating toner hardly adhere to the coating film 40 as a contaminant and, in addition, can be wiped off easily even when the vapor or toner adheres to the film 40.