PURPOSE: To equip a building with a vibration isolating function and allow easy recovery of the concrete mass from eventual displacement.

CONSTITUTION: A film 11 is installed between the concrete mass 2 of a building and the base structure 3 to bear the mass 2 so as to form a filling chamber 12 between the bottom 2a of the mass 2 and the top 6 of the base structure 3. This chamber 12 is filled with a fluid 4, and a pressurizing source 9c is installed to separate the undersurface 2a of the mass 2 from the oversurface 6a of the base structure 3 by pressurizing the fluid 4. The base structure 3 is provided with an actuator 5 which restrains the mass 2 in normal state, hinders the mass movement in the horizontal direction relative to the base structure 3, and disengages restraint when the base structure 3 vibrates with an amplitude ever a certain value.