An automatic driving assistance system to be applied to a vehicle includes an intersection detector and an ACC-set-vehicle-speed changing section. The intersection detector detects, on the basis of a traveling environment in a predetermined range of a target traveling course in front of the vehicle, a set of intersections whose interval is shorter than a predetermined interval within the predetermined range of the target traveling course in front of the vehicle. The traveling environment is to be acquired on the basis of road map data and traveling-environment data on an environment in front of the vehicle. The ACC-set-vehicle-speed changing section changes, in a case where the intersection detector detects the set of intersections whose interval is shorter than the predetermined interval, an ACC set vehicle speed from a first ACC set vehicle speed that is set to a second ACC set vehicle speed.