A driving assistance system performs a driver-initiative normal driving assistance mode as a driving assistance for a vehicle. The system includes a reaction force characteristics change unit configured to change reaction force characteristics of the operation device, if it is determined that the operation amount of the driver is not included in the appropriate operation amount range in the normal driving assistance mode, an explicit risk determination unit configured to determine whether or not an explicit risk is present based on the external environment of the vehicle, and a driving assistance switching unit configured to switch a driving assistance for the vehicle from the normal driving assistance mode to a system-initiative risk avoidance assistance mode, if it is determined by the explicit risk determination unit that the explicit risk is present in the normal driving assistance mode.