The present invention utilizes a vertically upward force of a water when a tsunami smashes into a building to close openings that exist in an elevated location such as air supply and exhaust ducts, powerlessly and without a manual operation. The present invention serves as a disaster prevention panel which closes an opening 2a disposed in a wall of a building 2. A door bumper 3 is disposed on an outer peripheral wall of the opening 2a, and side door bumpers 4 are disposed on both sides of the door bumper 3. A door body 1, which closes the opening 2a and which has a specific gravity lower than a seawater, is attached between the side door bumpers 4 on both sides so as to freely swing upwards, with a lower portion of the door bumper 3 serving as a fulcrum.