A seismic isolation mechanism 1 includes a seismic isolation apparatus 6 which is installed at one end 2 in a vertical direction V on a superstructure 3 and installed at another end 4 in the vertical direction V on a floor 5 serving as a foundation or a substructure to isolate the vibration of the superstructure 3 with respect to the floor 5; an attenuation damper 10 which is connected at one end 7 in the horizontal direction H to the superstructure 3 and connected at another end 8 in the horizontal direction H to a portion 9 of the seismic isolation apparatus 6 between the one end 2 and the other end 4 thereof to attenuate the vibration of the superstructure 3 with respect to the floor 5 as it is extended and contracted in the horizontal direction H; and an attenuation damper 13 which is connected at one end 11 in the horizontal direction H to the floor 5 and connected at another end 12 in the horizontal direction H to the portion 9 of the seismic isolation apparatus 6 to attenuate the vibration of the superstructure 3 with respect to the floor 5 as it is extended and contracted in the horizontal direction H.