PURPOSE: To obtain automatically the amount and the direction of birefringence.

CONSTITUTION: Light from a laser light source 1 is transmitted through an object 4 to be inspected as linear polarization by a 1/2-wavelength plate 2, is transmitted through a 1/4-wavelength plate 7, and is received by a CCD10 via an analyzer 8. Then, the polarization surface direction of the 1/2-wavelength plate 2 is matched to the phase-advance axis of the 1/4-wavelength plate 7 for synchronous rotation by motors 16 and 17, the analyzer 8 is rotated by a motor 18 at a plurality of rotation positions, and reception light data are obtained at a plurality of positions. The amount and the direction of birefringence of the object 4 to be inspected are calculated based on the light quantity detection data by a CPU 12.