To find a load-indenter indentation depth curve with precision of 1nm under an environment of 1000°C.

A single origin or a plurality of origins, which are common to the first coordinate system and the second coordinate system set in an observation system main body, are set. The first optical path, through which the first laser beams 17, 18 are advanced, is arranged among three points of the first reflection point and the origins, which are positioned the origin and in the first coordinate system and on a sample surface. While, the second optical path, which advances the second laser beam and shares the starting point and the terminal point with the first optical path, is set among three points of the second reflection point and the origins, which are positioned in the second coordinate system and fixed to an indenter touching the sample, and the origin. The first laser beams 17, 18 in the first optical path and the second laser beams 19, 21 in the second optical path are sent to a distance measuring means, fluctuation in a relative distance between the sample surface and an indenter is measured by means of the distance measuring means, and a dynamic relationship between a load and a displacement quantity is found with precision of 1nm.