Abstract: An isolaton floor system for accommodating the effects of an earthquake generally comprises a supporting floor and an isolation floor supported upon the supporting floor so as to be movable in at least one of the vertical and horizontal directions. A damper is interposed between the supporting floor and the isolation floor along the moving direction of the isolation floor. The relative displacement between both of the floors is adjusted by means of a lever or a pulley means to which springs are connected and which is operatively connected to the damper. A relative displacement direction changing mechanism may be further incorporated within the isolation floor system. A laminated rubber member provided with a predetermined shearing resistance is utilized for the damper. Any vibration caused by means of the earthquake is absorbed by means of the damper and the entire structure of the isolation floor system is prevented from being vibrated.