Progressive population aging has created many problems. Many aged people suffers from cataract because prevalence of cataract in advanced age is far higher than younger people. In this study, we have focused on N170 as a visibility-related signal for quantitative evaluation of cataract. In this report, basic evaluation of N170 in presenting numerical images which had different contrasts was performed. Amplitude and latency were extracted from N170, and then relations to the contrasts of the images were checked. The results showed that the experiments had feasibility, reproducibility and universality. It was also shown that there are positive correlation between logarithm of Michelson contrast and N170 amplitude, and negative correlation between log. contrast and latency.