A traffic lane deviation preventing system includes a traffic line detecting unit for detecting traffic line positions on a road, a control unit for determining a possibility of a vehicle's deviation from a traffic line based on the traffic line positions detected by the traffic line detecting unit and setting a travel target point to which the vehicle is to travel if it is determined that there is a possibility of a traffic line deviation. The control unit moves the travel target point toward the center of a traffic lane according to the passage of a control operation time.