A driving assistance device includes a determining part configured to determine a target relative position with respect to other vehicle, which is traveling in a movement destination lane that is a merging destination or a lane change destination of a host vehicle, for entering the movement destination lane based on a detection result of the other vehicle, and a notification controller configured to output a notification sound, which differs between a case in which acceleration is required for the host vehicle and a case in which deceleration is required for the host vehicle, from a speaker in order to perform an alignment with respect to the target relative position determined by the determining part in an advancing direction of the host vehicle.