An ellipsometer, which detects polarization of light successively reflected from a reference sample and an objective sample to study the objective sample, comprises first and second sample holder units for holding first and second samples, a beam projecting portion for projecting a beam of plane-polarized light toward the first sample, a polarizer, a turn-around prism for turning around the light beam reflected from the first sample to direct it to the second sample, an analyzer, a light detector for detecting light transmitted through the analyzer, and a sample positioning mechanism for arranging the first and second samples at appropriate positions and in appropriate orientations. The sample positioning mechanism includes one of the first and second sample holder units, which holds the objective sample, and comprises a height/inclination adjusting section for adjusting height and inclination of the objective sample.