To control maximum displacement during operation and residual displacement after operation by adding restoring function to a hydraulic cylinder type damper that is used for a base-isolating type isolation structure.

When a hydraulic cylinder as a damper which is another structural element of a base-isolating type isolation structure is used, restoring force is obtained by repulsion force against compression of a gaseous body so that hydraulic oil of two chambers separated by a piston is respectively led to airtight containers. The containers are preloaded in advance, and the containers act on a surface of the piston as a mechanism only when the piston is located on a pressurizing position, and restricting force at a neutral position of the piston is enlarged. Further, if a pre-stressed spring is utilized instead of the gaseous body and its preloaded condition of the containers, a burden of maintenance is remarkably reduced.