Human visual system has been evolving through the long history of human being and has attained very high performance. However, artificial system is often poorer in performance despite of remarkable progress in their efficiency. In order to construct artificial vision system with high performance such as human visual system, it is necessary to elucidate the mechanism of human visual system. In this study, two experiments were designed in order to investigate the relationship between the subjective contours strength and the curvature of the illusory form. Both of the two experiments used the partial eclipse disc as the inducing elements, while the illusory form was an ellipse. Experimental stimuli were those figures whose one inducing element was randomly emitted from the standard figure. In Experiment I, the area of the inducing element was bigger where the curvature of the illusory form was smaller. We got the result that that the mean subjective contours strength is stronger when the curvature of illusory form of omitted inducing element is smaller. In Experiment 2, although the area of the inducing element was bigger where the curvature of the illusory form was bigger. The experimental results showed that the conclusion of experiment 1 was still tenable in this different case. The results of psychological experiments will be significant to investigate the mechanism of human visual information processing and to construct an artificial vision system for pattern recognition.