In this paper, in order to investigate a contact area between the measured profile of wheel and the designed shape of rail, we carried out calculation of the contact area strictly by a general software program, which applied the boundary element method and half-infinite body approximation. In addition, a calculation method of a creep coefficient is proposed with focus on contact areas between actual wheel and rail. Moreover, we also carried out numerical simulation of the running stability to find out how the difference of a value of an estimated creep coefficient has influence on the running stability of railway vehicle. As a result, it is shown that the contact area between the actual wheel and the rail has the shape composed of many contact areas, and the estimated creep coefficient may be smaller than the Kalker's theoretical value due to the influence of fine unevenness of wheel tread. Furthermore, we describes that the proposed method make the evaluation on running stability on the safety side.