PURPOSE: To make contactless measurement possible and to reduce the influence of the emissivity of an object to be measured to measure the temperature of even the object having a low emissivity with high precision, by making the heat radiation from the object to be measured incident into an inside tube, and detecting temperature of the inside tube and an outside tube when the inside tube is heated near the temperature of the object to be measured and obtaining the surface temperature of the object to be measured.

CONSTITUTION: An aperture part 14 of a radiation-type temperature detector 10 is arranged to face closely an object 30 to be measured, and heat radiation from the object 30 to be measured is made incident into an inside tube 12 from the aperture part 14. The temperature in the inside tube 12 rises up to a temperature near the surface temperature of the object 30 to be measured by heat radiation. In this state, the temperature of the inside wall of the inside tube 12 and that of an outside tube 18 are detected by thermocouples 22 and 23. The surface temperature of the object 30 to be measured is calculated on a basis of the temperature of the inside wall of the inside tube 12 and that of the outside tube 18 which are detected by thermocouples 22 and 23. Such procedures are required as a double tube 11 is formed into a very shallow cavity such as a hemisphere or the like and an inside surface 11A of the double tube 11 is subjected to silver plating or the like to make the emissivity lower.