To provide a back focal plane microscopic ellipsometer which obtains a further accurate optical constant and a film thickness of a sample in consideration of contribution of an objective lens by determining accurate polar coordinates of a back focal plane to correct non-uniformity of a light intensity due to a device.

An incident optical system 6 includes a first lens system 10 which makes parallel light impinge on an object lens 1, and a first polarizer 11, and an emission optical system 7 includes a second polarizer 12 and a second lens system 14 which forms an image of a back focal plane 3 of the objective lens 1 on a two-dimensional detector 13. A background image of the back focal plane is acquired and is used to discriminate an outline of emitted light, polar coordinates of the back focal plane are determined, and a measurement image is standardized by the background image, whereby unevenness of the light intensity due to a device is corrected. An incident angle and an azimuthal angle dependence which reflect characteristics of a sample and the objective lens are detected, a plurality of polarization analysis parameters different by incident angles are calculated, simultaneous fitting at a plurality of incident angles is performed in consideration of contribution of the objective lens, and an optical constant and a film thickness of the sample are obtained.