PURPOSE: To provide a vibration isolating base position control method which can control an object to be controlled completely regardless of the mounting accuracy of a vertical directional displacement sensor fixed onto a supporting element or the object to be controlled.

CONSTITUTION: Displacement signals S1, S2, S3, S4 actually measured between an object to be controlled and a supporting element while the object to be controlled on a vibration isolating base 1 is in a down condition are stored in a control circuit 6, and a displacement between the predetermined object to be controlled and the supporting element is subtracted from the target value of the floating mount while the object to be controlled is in down condition. The subtraction value is added to an actually measured displacement which is stored in the control circuit 6, and the added figure is stored in the control circuit 6 as a new target value of floating amount. A detecting distance detected by contactless vertical displacement sensors 5a, 5b, 5c, 5d is controlled so as to obtain the new target value of floating amount stored in the control circuit 6 while the object to be controlled is floating. Therefore, pneumatic springs 4a, 4b, 4c, 4d are feedback-controlled through an electropneumatic analog valve 7 based on a control signal S5 from the control circuit 6.