PURPOSE: To improve both the comfortability and steering of a car by forming two fluid rooms in an elastic bush inserted between a car body and a suspension arm and controlling the move of a fluid between two fluid rooms according to the running conditions of the car.

CONSTITUTION: When a car travels straight, the ground surface of tire 24 is vibrated by the displacement that contains many frequency components. In this case, a channel is kept open and a fluid freely flows from one room 13 to the other room 14. Therefore, the spring constant of an elastic bush 12 stuck on the inner surface of a collar 11 at the end of a trailing arm 10 is reduced and the comfortability of a car is improved. On the other hand, when the car is rotated and the lateral acceleration (lateral G) of the car exceeds a preset value, the result is detected by a lateral G sensor 23 and signals are output to a control circuit 22. As a result, since an electromagnetic valve 20 squeezes and closes the channel 19, the fluid of both the rooms 13 and 14 is actuated as rigidity or semi-rigidity. Besides, the spring constant of the elastic bush 12 is increased and the steering of the car is improved.