A driving assistance device of one embodiment includes an acquirer that acquires first environmental information representing an environment of a traveling point of a vehicle after elapse of a given length of time from a current traveling point of the vehicle, a check information storage that stores second environmental information representing an environment of a point at which the vehicle has traveled and check action information representing a driver's necessary action under the environment indicated by the second environmental information, in association with each other, an action information storage that stores third environmental information and actual action information representing an actual action of the driver under the environment indicated by the third environmental information, in association with each other, a comparer that compares the check action information, which is associated with the second environmental information of the environment indicated by the first environmental information in the check information storage, with the actual action information, which is associated with the third environmental information of the environment indicated by the first environmental information in the action information storage, and a notifier that issues a notification on the basis of a result of the comparison by the comparer.