Eddy Current Testing (ECT) is widely used for non-destructive testing in the industrial fields. Furthermore, ECT is expected to be used not only for evaluating the integrity of products, but also in the field of fundamental research, such as the mechanism study of hydrogen assisted fatigue crack growth since ECT can evaluate electromagnetic properties. However, the low spatial resolution of ECT is an issue for such applications. To improve the resolution of ECT system, a magneto-optic (MO) element is applied to the receiver part of ECT instead of the pick-up coil. In this system, the noise introduced into the section measuring the rotation angle of the polarization plane is an issue. To reduce this noise, the MOECT system that employs polarization beam splitter is constructed in this study. As the first step, the detection capability of the MOECT system is investigated by detection test on the through slit, and the validity of the result in the detection test is confirmed by analysis.