Warning information that facilitates grasping an obstacle located in rear of a vehicle is provided. A driving assistance system including: a first detection section that detects an obstacle from a plurality of captured images of a rear side of a driver of a vehicle; a second detection section that detects the obstacle by analyzing a reflected wave of a measurement wave transmitted to the rear side; and an information output section that determines a direction in which the obstacle is located with respect to the vehicle on the basis of detection results of the first detection section and the second detection section, and that outputs warning information indicating the direction.