This automatic steering system of an automobile has two remarkable features: (1) a course deviation at some distance ahead of the automobile is detected, (2) the steering angle is controlled in proportion to the course deviation. This paper describes how three parameters, i.e. L, detecting distance of the course deviation, ka, the gain constant of the proportional control and V, the vehicle speed (under 30km/h), affect on the characteristics of the system. The conclusions are as follows. (1) This system is stable for L over some region when ka is smaller than a certain critical value determined by V. (2) The stable region of the system becomes nallow with the increase of V. Practical tests of the system have been performed giving the reference course a step and a straight configuration on the road surface. The tests have shown the possibility of the automatic automobile steering using the information of a course deviation at some distance ahead of the automobile.