To establish a technique for the high-reliability calibration of a temperature sensor under a high-temperature condition.

In a short time, a laser is irradiated at a standard product 5F (not shown in the figure) and a thermocouple 5S as an object to be calibrated. The intensity q/a of the laser at this time is measured, where (a) represents parameter as an average constant. Respective temperature change amounts T1(t), T2(t) are input to a computer. A function F1(t-τ)Q1(t) and a function F2(t-τ)Q1(t) which use laser intensities Q1(t). Q2(t) as factors are integrated respectively regarding a variable τ while an integration range is set as a time width, the temperature change amount of the first sample 5F and that of the second sample 5S are divided by amounts which have respective integral values as factors, amounts which have first factors of known physical property values and unknown constants of the first sample 5F and the second sample 5S are calculated, and the unknown constants are found as known constants. Since a physical property value as an unknown, the parameter (a), a physical property value as a known and the parameter (a) are substituted in two isomorphic forms of an identical system, both unknowns are found analogically. A calibration value which is found analogically from isomorphic functions is of high reliability in the system.