In usual measurement with the Sènarmont method using a conventional polarization microscope, the azimuth angle of the analyzer at extinction of the emerging light is detected by naked eyes. If the intensity of light is measured as a function of the azimuth angle of the analyzer, one can find the direction at which the intensity is minimized more accurately by fitting. However, this procedure requires much numbers of operations as compared to the usual method, and thus is time-consuming. To circumvent this problem a setting with which the intensity is measured as a function of the azimuth angle of the analyzer is constructed with rotation of the analyzer through a computer control. As a result, the time required for the measurement has been greatly decreased.