In a driving assist system, a driving assist device as a control device acquires driving control information to be used for performing a driving control process in which an own vehicle follows a preceding vehicle running on the same lane of the own vehicle in front of the own vehicle. The driving assist device performs the driving control process of the own vehicle based on the acquired driving control information. The driving assist device detects an interruption of a preceding-vehicle following of the own vehicle. In the preceding-vehicle following, the own vehicle follows the preceding vehicle running on the same lane. The driving assist device decelerates a vehicle speed of the own vehicle by using a predetermined braking force when detecting the interruption of the preceding-vehicle following of the own vehicle during the preceding-vehicle following.