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 generator for generating a gravity point distribution image based on a smoothing process of a pattern in the first image or an exposure simulation of the pattern, pixel values of the gravity point distribution image respectively varying with distance from a gravity point which is a center of a two dimensional region indicating pattern shape in the gravity point distribution image; a matching score calculator for calculating a matching score based on the gravity point distribution image and contour data formed from the second image; and a maximum score position detector for detecting a position where the matching score becomes the maximum.