For the controller of the auto step unit, which operates in conjunction with the opening/closing operation of the left sliding door, to make entering/exiting the vehicle easier, it may mistakenly identify that the vehicle has started, when the brake pedal is pressed more than twice a second, even while the engine is stopped and the auto step is extended out, due to a program glitch. If this occurs, the fail-safe function may activate, and in the worst case, the step might be put away while a passenger is trying to enter/exit the vehicle.