PURPOSE: To improve the positioning precision of an object to be controlled by memorizing respective detecting distance with respective horizontal displacement sensors as targets while the object to be controlled is in a stationary condition, and controlling the detecting distances with the respective horizontal displacement sensors so as to obtain the memorized targets at the time of the horizontal displacement of the object to be controlled.

CONSTITUTION: In a vibration isolating base 1 which supports the object to be controlled such as a surface plate where a precision instrument is installed onto a supporting base such a foundation, the displacement signals S1, S2 of a detecting distance detected by horizontal displacement sensors 4a, 4b fixed at a relative position to the object to be controlled are stored in a control circuit 6 as target values while the object to be controlled is in a stationary condition. At the time of the horizontal displacement of the object to be controlled, control circuit 6 outputs a control signal S3 for controlling the respective detecting distances so as to obtain stored target values to feedback-control horizontal actuators 5a, 5b through an electropneumatic analog valve 7. It is thus possible to control the object to be controlled so as to obtain the position of the stationary reference point.