A driving assistance device of an embodiment includes a recognizer configured to recognize a surrounding situation of a mobile object, a determiner configured to determine, on the basis of the surrounding situation, whether to prompt a driver of the mobile object to perform a steering operation and whether there is a possibility of a risk occurring for the mobile object, and a notification controller configured to cause a speaker to output a guidance sound prompting the driver of the mobile object to perform a steering operation and a warning sound with respect to the risk on the basis of a result of the determination by the determiner, in which the notification controller causes output modes for the guidance sound and the warning sound to be different from each other.