Driving assist control has plural control modes associated with plural scenes on a one-to-one basis. A scene corresponding to driving environment for a vehicle is a subject scene, and a selected control mode is one associated with the subject scene. Plural pieces of scene description information respectively define the plural scenes. Selected scene description information is one defining the subject scene and indicates parameters used in the driving assist control of the selected control mode. A processor executes the driving assist control of the selected control mode based on the parameters indicated by the selected scene description information, and switches the selected control mode by switching the selected scene description information. When the subject scene changes, the processor notifies an occupant of the vehicle of switching of the selected control mode before switching the selected scene description information and the selected control mode.