PURPOSE: To enable accurate positioning by detecting encoded radiant energy by a sample which is adjacent to an ATR(attenuation total reflection) crystal body in observation mode and analyzing the sample in analytic mode by using the encoded radiant energy.

CONSTITUTION: In the observation mode, the surface of the sample 26 can be observed through an observation port 13 along an optical path passing through a Cassegrain object and ATR crystal 22. In this case, the observation can selectively be made only by changing an incidence and an exit aperture which changes an incidence angle and a reflection or radiation angle without moving the sample 26. In the analytic mode, narrow-band radiant energy from a light source 3 is made incident on the sample 26 through the aperture of an incidence mask 18 and the crystal 22. Energy reflected or emitted by the crystal 22 is reflected by primary and secondary optical elements 21 and 20 and passes through the exit aperture of the mask 23, and the energy is encoded with the information of the sample 26 because of energy absorption by the sample 26 and made incident on a detector 25.