DRIVING ASSISTANCE DEVICE, DRIVING ASSISTANCE METHOD, AND STORAGE MEDIUM

According to an embodiment, a driving assistance device includes a recognizer configured to recognize a surrounding situation of a mobile object, a decider configured to decide whether or not to prompt a driver of the mobile object to perform acceleration or deceleration on the basis of the surrounding situation, and a notification controller configured to cause a speaker to output a notification sound for prompting the driver of the mobile object to perform the acceleration or deceleration on the basis of a decision result. The notification sound is a notification sound obtained by continuously changing a structure of a sound.