Oppositely of a temperature measuring surface of an object-to-be-measured 16, a reflecting member 28 is disposed while being spaced by a reflection gap 35 from the temperature measuring surface. The reflecting member 28 is composed of a heat
ray reflecting material capable of reflecting heat
ray in a specific
wavelength band, in a portion including a reflection surface 35a. A heat
ray extraction pathway section 30 is disposed through the reflecting member 28 so that one end thereof faces the temperature measuring surface. Heat ray extracted through the heat ray extraction pathway section from the reflection gap is detected by a temperature detection section 34. The heat ray reflecting material is configured in a form of a stack comprising a plurality of element reflecting
layers composed of a material having transparent properties to the heat ray, in which every adjacent two element reflecting
layers are composed of a combination of materials having refractive indices which differ from each other by 1.1 or more. This makes the measurement be hardly affected by
radiation ratio of the object-to-be-measured when temperature of the object-to-be-measured is measured by a
radiation thermometer, enables to measure its temperature more correctly irrespective of the surface state thereof, and can simplify configuration of a measurement
system.