A driving assistance device is the driving assistance device 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 that acquires autonomous driving information on different vehicles on a traveling road of the vehicle, an autonomous driving ratio acquisition unit 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, and a notification control unit 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.