DRIVING ASSISTANCE DEVICE, DRIVING ASSISTANCE SYSTEM, DRIVING ASSISTANCE METHOD, AND PROGRAM

To assist a driver in making an appropriate determination on switching between autonomous driving and driving that requires operation by the driver. A driving assistance device 10 is the driving assistance device 10 used in a vehicle capable of switching between autonomous driving and driving that requires operation by the driver, and includes a different vehicle information acquisition unit 23 that acquires autonomous driving information on different vehicles on a traveling road of the vehicle, an autonomous driving ratio acquisition unit 24 that acquires a ratio of autonomous driving in the different vehicles from the autonomous driving information on the different vehicles acquired by the different vehicle information acquisition unit 23, and a notification control unit 26 that provides information for supporting determination on switching between autonomous driving and driving that requires operation by a driver if the ratio of autonomous driving in the different vehicles is equal to or larger than a predetermined ratio.