To provide an impact mitigation technique to the rubble and a rocking control technique to a "floating body type flood damage evacuation shelter that substitutes the height" for securing safety of accommodated evacuees.

Problems of impact reduction and rocking control are solved by: installing an evacuation chamber 1 of a spherical shell shape in a central part of a shelter; installing a gap in the periphery of the evacuation chamber 1; installing a buoyancy body 2 in the periphery of the gap; connecting a protection body 3 to the buoyancy body 2; loosely connecting the evacuation chamber 1 with the buoyancy body 2 using a shock absorber 4; preventing adhesion of the rubble by making the buoyancy body 2 rotatable in the horizontal direction of the evacuation chamber 1; further making the evacuation chamber 1 a gimbal structure; maintaining the evacuation chamber 1 vertical by making the evacuation chamber 1 three dimensionally rockable against the tsunami; further connecting the shelter and the foundation ground with the connecting rope; and providing a means to separate the connecting rope when there is a risk of adhering the rubble to the shelter.