sprung acceleration a signal from a damper displacement sensor sb for sensing displacement stroke of the damper 14 a signal from a lateral acceleration sensor sc for sensing the lateral acceleration of the vehicle and a signal from a vehicle vehicular speed sensor sd for sensing vehicle speed are input into an electronic control unit u that controls damping force of the damper 14 as shown in fig2 the damper 14 has a cylinder 21 whose lower end is connected to the suspension arm 13 a piston 22 fitted slidably into the cylinder 21 a piston rod 23 extended upward from the piston 22 to pass through an upper wall of the cylinder 21 and connect its upper end to the vehicle body and a free piston 24 fitted slidably into a bottom portion of the cylinder an upper side first fluid chamber 25 and a lower side second fluid chamber 26 are partitioned by the piston 22 in the cylinder 21 and also a gas chamber 27 into which a compressed gas is sealed is partitioned under the free piston 24 a plurality of fluid passages 22 a are formed in the piston 22 to cause an upper surface and a lower surface to communicate with each other and.