To adjust the height of level by a variable adjustment parameter, and to improve a control characteristic, by installing an electric control-type flow control valve which is controlled through an electronic controller on the basis of an output signal of a non-contact operation-type distance sensor, on a high pressure air supply passage of an air spring.

An object 1 is supported on a base 3 through an air spring 2 for the vibration isolation, and an induction-type sensor 4 as a distance sensor, is installed therebetween. And the sensor signal is input to the electronic controller 5, and an output signal of the electronic controller 5 is supplied to an electric control-type flow control valve 6 installed on a high pressure air supplying passage 7 of the air spring 2, to control the high pressure air supplying amount to the air spring 2. The induction-type sensor 4, the electronic controller 5, and the electric control-type flow control valve 6 form an adjusting circuit for adjusting the level of the object 1 without using the mechanical shunt to the base 3, so that the control characteristic of the vibration isolation, can be improved.