For example, in the case of Level 1, the automated driving system 2 evaluates a possibility of unscheduled travel behavior such as lane change, U-turn, and parking/stopping and causes the vehicle image display system 1 to display prior notice to prompt a driver to perform selection. In the case of performing only accelerating, the automated driving system 2 performs an accelerating operation in accordance with a steering and/or braking operation of the driver when lane change or the like is selected by the driver. Further, the automated driving system 2 of Level 1 performs steering in accordance with an accelerating and/or braking operation of the driver in the case of performing only steering, and performs braking in accordance with as accelerating and/or steering operation of the driver in the case of performing only braking. Thus, the automated driving system 2 of Level 1 assists an unscheduled travel behavior selected by a driver.