A seismic isolation device comprises a floor body which is arranged on a structural floor and to which an object of seismic isolation is mounted, a first restoring member disposed on the structural floor and adapted to impart a horizontal restoring force to the floor body when the floor body is horizontally displaced with respect to the structural floor, a first damping member arranged in association with the first restoring member and adapted to impart a horizontal damping force when the floor body is horizontally displaced with respect to the structural floor, a first engaging member projecting from the floor body towards the structural floor, a second engaging member provided on the first restoring member and sliding while coming into contact with the first engaging member, a second restoring member disposed to a lower portion of the floor body and adapted to impart a vertical restoring force when the floor body is vertically displaced with respect to the structural floor, a second damping member arranged in association with the second restoring member and adapted to impart a vertical damping force when the floor body is vertically displaced with respect to the structural floor, and a support mechanism for supporting the floor body to be movable in a horizontal direction.