A driving assist device comprises an electronic control unit configured to: acquire a vehicle present position that is a position at which a vehicle is present; calculate a positional relationship between a lane increase-decrease area and the vehicle, based on the lane increase-decrease area position and a vehicle present position; cause a human machine interface to output information about the lane increase-decrease area when a positional relationship is determined to satisfy a predetermined condition; acquire information about a traveling lane in which the vehicle is traveling; and cause the human machine interface to vary a way to output a information, based on whether or not the lane including the lane increase-decrease area and the traveling lane coincide with each other.