PURPOSE: To increase roll rigidity and improve running stability, by limiting a degree of communication of a suspension fluid chamber between lateral two wheels in accordance with a car speed.

CONSTITUTION: Pressure air from an air tank 6 is supplied to and discharged from rear two wheel suspension units 1, 1' and front two wheel suspension units 23, 23' by air introducing solenoid valves 13, 13' or pneumatic pressure release solenoid selector valves 17, 17' to adjust car height. A signal from car height sensors 3, 3' is input to a controller 4, while a car height signal from a car speed sensor 27 ia also input. A normally close solenoid valve 26 and normally open solenoid valve 26' open and close communication passages 25, 25' between air chambers in accordance with a car speed by the controller 4. In this way, roll rigidity of a car body can be increased, and a steering characteristic is changed to enable the improvement of running stability.