Establishing breakwaters in Japanese ports have greatly improved the calmness in ports. However, the seawater exchange between landward and seaward areas in ports has greatly decreased. In ports near urban areas, the inflow of sewage or industrial wastewater and the accumulation of sludge are causing a variety of environmental problems. To realize a seawater exchange breakwater that will improve the calmness in ports and the seawater exchange, an armored caisson breakwater with intake holes was developed to allow fresh seawater into the port using wave energy. The armored caisson breakwater with an opening ratio of 16.8% is under construction in Kudoh fishing port on the Sea of Japan. In this paper, the characteristics of seawater exchange and wave transmission of this breakwater introduced based on the results of 2-D & 3-D model tests and numerical simulations.