To contemplate doing its simplification with respect to designing the mounted equipment, and also to contrive the strutural simplification and inexpensiveness in cost.

This vibration isolating device is equipped with a support mount 3 mounting precision equipment and an air spring 4 being disposed in space between this support mount 3 and a reference plane and absorbing any vibration of the precision equipment, and this air spring 4 is comprised of two bellows 4a and 4b whose each spring constant is variable by on-off operation of an adjusting valve 5 due to vibration in the support mount 3 in terms of structure.