An object is to prevent a driving assistance system for a vehicle from causing a collision of the driver's own vehicle with a solid object by performing driving assistance. To achieve the object, when a solid object that can be an obstacle exists in the course of the driver's own vehicle, the driving assistance system for a vehicle according to the present invention determines a plurality of primary paths along which the driver's own vehicle can travel by changing the momentum thereof, designates an avoidance line along which the solid object can be avoided from among the primary paths, and changes the momentum of the driver's own vehicle in such a way that the driver's own vehicle travels along the selected avoidance line. If the plurality of primary lines do not include an avoidance line, the driving assistance system sets a divergent point in the middle of the primary paths and determines a plurality of secondary paths along which the driver's own vehicle can travel by changing the momentum of the driver's own vehicle at the diverging point. Then, the driving assistance system selects an avoidance line from among the plurality of secondary paths.