A driving assistance device includes a deceleration detection unit, an information calculation unit, and an index calculation unit. The information calculation unit obtains at least one type of front information including a time to collision until an own vehicle collides with a preceding vehicle, a time headway until the own vehicle reaches a position of the preceding vehicle, and a following distance between the own vehicle and the preceding vehicle when the own vehicle stops, after a deceleration start of the own vehicle. The index calculation unit obtains an index indicating a driving characteristic that is a characteristic of a driving operation of a driver, based on the front information.