An object of the invention is to provide, in a vehicle driving assistance system that provides assistance to avoid a collision between a host vehicle and a three-dimensional object causing an obstruction, a technique for avoiding assistance in which the host vehicle is guided to a region where the presence of a three-dimensional object is unclear. To achieve this object, according to the invention, a grid map, by which an avoidance region in which a three-dimensional object exists, an unclear region in which the existence of a three-dimensional object is unclear, and a safe region in which no three-dimensional objects exist can be distinguished, is created. When the avoidance region exists on the advancement path of the host vehicle, a route that can avoid the avoidance region and passes through the unclear region for a distance not exceeding a threshold is specified, whereupon a steering angle is controlled to cause the host vehicle to travel along the specified route.