A driving assistance device includes: a vehicle group search unit that acquires a most frequent vehicle speed of the vehicle and to search for one or more vehicle group, the most frequent vehicle speed being a vehicle speed that is most frequent, the vehicle group traveling at one of the most frequent vehicle speed and a speed close to the most frequent vehicle speed; a distance information generation unit that generates the vehicle group searched for by the vehicle group search unit and distance information on a distance between the vehicle group and an information-receiving vehicle that has sent the most frequent vehicle speed; and a merging assistance unit that sends the distance information generated by the distance information generation unit to a user terminal device and assists the vehicle in merging into one of the vehicle groups searched for by the vehicle group search unit.