PURPOSE: To prevent the air balance panel from interfering with the ground by a structure wherein the driving mechanism to vertically movably drive the air balance panel installed at the lower part of a vehicle is controlled in association with car level, panel height and car speed.

CONSTITUTION: The air balance panel 1 is pivotally attached to a supporting bar fixed to a car body and vertically moved by means of a screw rod 6 driven by a motor M. The motor M is controlled by means of an electric control unit 16. Concretely, the electric control unit 16 receives the output signal of the potentiometer 14 of a car level sensor, the voltage signal of the potentiometer 10 of a panel altitude detector and a car speed signal and controls the motor M by driving so as to lower the air balance panel 1 in case that the car speed exceeds the predetermined value and the car level is high and to raise the air balance panel 1 in case that the car speed is lower than the predetermined value.