Provided is a flood prevention dam that can prevent overflow even when high waves are surging and that can prevent overflow by a high wave without being large. A flood prevention dam 1 comprises a bottom sheet 2 and a dam wall 4 each made of a waterproof cloth, and the back end of the bottom sheet 2 and the bottom end of the dam wall 4 are integrally formed by way of the flexibility of the waterproof cloth with the dam wall able to change from a collapsed state to an erect state. The dam wall 4 is provided with core plate housing sections 5, and core plates 6 are accommodated from a location near the bottom end to a location near the top end of the dam wall 4. The flood prevention dam is provided with an opening angle limiting member 7 that limits the angle when the dam wall 4 is erected by joining the top face of the bottom sheet 2 and the front face side of the dam wall 4.
