The invention relates to the flexible joint water-proofing plate of the concrete structure, and more particularly to the flexible joint water-proofing plate of the concrete structure which enhances the rigidity through the material improvement and reinforcing rib and it is not flown in the during concrete casting through the fastening with the steel reinforcement in the predetermined position and can enhance the quality of construction in the construction. For this, in the flexible joint of the concrete structure, as long as the padding construction is comprised of one side and the other side of the concrete structure which each other is faced the wing portion formed between a pair of wing portions of the wing portion: pair of pair is integrated and it is formed in the man outer end of the hollow expansion portion: wing portion which is provided in order to be newly built according to the gap change of the concrete structure, and the wing portion is formed between the projection part: projection part which is protruded from the wing portion to the either side and prevents in the expansion portion expansion function that the wing portion is slipped within the concrete structure and expansion portion into the plurality and it is protruded from both sides of the wing portion and the reinforcing rib reinforcing the rigidity of the wing portion is formed in the expansion function and the reinforcing rib is formed to the expansion portion and the expansion portion is formed into the first hollow part, and the second hollow formed in the bilateral wing part of the first hollow part based on the first hollow part and the flexible joint water-proofing plate of the concrete structure in which the diameter of the first hollow part is formed in comparison with the diameter of the second hollow is provided.