PURPOSE: To embody a high wave killing effect and maintain the low execution cost.

CONSTITUTION: In a wave killing structure 1 constructed so that a flow part 3 comprising a longitudinal slit is formed on the front of a concrete-caisson breakwater, and a retarding part 2 having a designated length and depth of water is formed on the inside thereof, there are provided partition walls 5 which are continuous in the direction of normal and have a height near the water surface in the vicinity of the center between the flow part 3 and the rear wall 4 of the retarding part 4. The partition wall 5 has a function of further disturbing a flow disturbed by a slit of the flow part 3 in the vicinity of the water surface of the partition wall 5 without obstnucting the effect of reducing the reflectance due to the phase difference in the rear wall 4 of the retarding part. Thus, increase in the execution cost can be suppressed with a simple structure.