It is indispensable to grasp geometrical characteristics of contact point between wheel and rail to analyze the characteristics of vehicle dynamics. However, there has not been an analytical method capable of calculating simply and easily geometrical characteristics of contact point, which is formed by actual shapes of worn tread running surface of rail and wheel tread. Therefore we have developed an analytical system by which we can calculate variations of wheel radius and contact angle each corresponding to lateral displacement of a wheel set for a combination of worn wheel tread and worn rail running surface, and finally, equivalent conicity can be obtained based on the results of calculation.