PURPOSE: To provide a polarization analyzing instrument which can make highly accurate measurement.

CONSTITUTION: A λ/2- and λ/4-plates 4 and 5 respectively rotated and controlled by means of driving sections 41 and 42 are arranged on the optical path connecting a light source to a sample S and a beam splitter 6 is provided on the optical path in the direction in which the light from the light source 1 is reflected by the sample S. Then analyzers 7 and 8 which only transmit one of vibrating components in orthogonal two directions and reflect the other component are respectively provided in the transmitting and reflecting directions of the beam splitter 6. In addition, photoelectric detectors 9-12 are respectively provided in the transmitting and reflecting directions of the analyzers 7 and 8. The detectors 9-12 are connected to a preamplifier board 13 which amplifies the outputs of the detectors 9-12 and the board 13 is connected to a polarization characteristic calculating section 14 which calculates the polarization characteristics of the sample S from the output of the board 13.