PURPOSE:To make it possible to measure the radiation temperature accurately at a low cost, by setting the emissivities of radiation thermometers, which are provided at points other than a reference point, based on a temperature characteristic curve corresponding to the emissivity, which is measured at the reference point. CONSTITUTION:A furnace temperature T is measured by a thermocouple 9, which is provided at a reference point D. By using an indicated temperature S of a radiation thermometer 4 at the reference point D, an emissivity xsi is obtained in an operating part 10 by using an expression in the Figure (where lambda is the effective length of the radiation thermometer and C2 is the second constant of Planck). The emissivity xsi, which is obtained in this way, is sent to a comparing part 11. Based on the comparison, a value, which is most close to the temperature characteristic curve of the emissivity, is selected from a memory part 2. The emissivity value at each temperature is sent to converter parts 13-16 of radiation thermometers 3, 5-7, which are provided at other positions, based on the selected temperature characteristic curve of the emissivity. Based on the outputs of the radiation thermometers 3, 5-7, the temperatures of the steel plate are indicated on display parts 17-20.
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