1. An image processing system for carrying out a pattern matching between a first image and a second image, comprising: a gravity point distribution image generation means for generating a gravity point distribution image based on the first image; an edge line segment group generation means for generating a group of edge line segments based on the second image; a matching score calculation means for calculating a matching score based on the gravity point distribution image and the group of edge line segments; and a maximum score position detection means for detecting a position where the matching score becomes the maximum.