To provide a spectroscopic ellipsometer which has high accuracy of measurement.

An illumination part 3 of the spectroscopic ellipsometer 1 has a measuring light source 31. A polarized light, which is obtained by a polarizer 32 from a light of the measuring light source 31, is led to a substrate 9. A light-receiving part 4 has an analyzer 41, on which a reflected polarized light from the substrate 9 is incident. The reflected polarized light which has passed via the analyzer 41 is incident on a spectroscope 42, then a polarized status for every wavelength is obtained. In the spectroscopic ellipsometer 1, a mirror is arranged only at positions between the measuring light source 31 and the polarizer 32 and between the analyzer 41 and the spectroscope 42. According to above arrangement, in the spectroscopic ellipsometer 1, there is no change by the mirror in the polarized status for the polarized light and the reflected polarized light, so that high accuracy measurement is realized.