PURPOSE: To raise measuring accuracy of a thermo-electromotive force by irradiating infrared rays or visible light to an object to be measured, such as a semiconductor, a metal, an insulator, etc., and giving a sudden temperature difference to the upper and lower faces of the object to be measured.

CONSTITUTION: Chromel - alumel thermocouples 20, 21 are fixed so electrical that they come into contact with the upper and lower faces of an object to be measured 4. Alumel side leader lines A1, A2 of each thermocouple 20, 21 are immersed in a cold contact 22 held at 0°C. A thermo-electromotive force is measured by lighting for a prescribed period light sources such as a halogen lamp, a laser light generator, an infrared ray light source, etc. provided so as to be opposed to the upper face of the object to be measured 4, irradiating light to the upper face of the object to be measured 4, and giving a temperature difference between the upper face and the lower face of the object to be measured 4. The measurement is executed at an optional time in a period in which this temperature difference exists. For instance, when deriving a Seebeck coefficient S with high accuracy, it is derived by S=dV/d(ΔT) from a difference d(ΔT) of a temperature difference ΔT in a measured value of two points and a difference dV in a thermo-electromotive force, or can be derived by the method of least square, etc. from a lot of measured values.