PURPOSE: To obtain temperature-thermoelectromotive force characteristics accurately in a high temperature region without measuring a Pd point under the equal state, wherein the measured value at the Pd point is added.

CONSTITUTION: An R thermocouple is calibrated at the at least one point of a Zn point and an Al point and two points among an Au point, an Ag point and a Cu point. The result and the deviation from the Table of JIS-C-1602 are regressed by the method of least square by a quadrative expression, and the value is extrapolated into a high-temperature region.