Each of a plurality of autonomous driving vehicles configuring an autonomous driving system executes lane selection determination processing of acquiring information concerning an empty space situation in an adjacent lane that is adjacent to a lane where an own vehicle is traveling, and determining whether or not to select the adjacent lane as an own vehicle travel lane in accordance with an empty space situation in the adjacent lane. When the adjacent lane is selected as the own vehicle travel lane by the lane selection determination processing, lane change to the adjacent lane is performed autonomously, or lane change to the adjacent lane is proposed to a driver. The autonomous driving system gives variation to an execution interval of the lane selection determination processing among the plurality of autonomous driving vehicles.