In steel strip surface inspection, high discrimination capability of extracting harmful defects by suppressing excessive detection such as harmless oil patterns is required. Firstly we estimate the relative intensity profiles along azimuth angle of polarized light reflection of surface objects. Secondly we execute experiments with rotating analyzer, finding that defects and oil patterns have different polarity of intensity to the normal surface in polarized images. Finally we bring the technique into practice as a real-time on-line inspection equipment and prove the effective function discriminating excessive-detection matters from real defects.