In a seawater desalination system for producing fresh water from seawater by passing the seawater pressurized by a pump through a reverse-osmosis membrane-separation apparatus to separate the seawater into fresh water and concentrated seawater, an energy exchange chamber for utilizing pressure energy of the concentrated seawater discharged from the reverse-osmosis membrane-separation apparatus as energy for pressurizing part of the seawater is provided. The energy exchange chamber includes a concentrated seawater port for introducing and discharging the concentrated seawater, a seawater port for introducing and discharging the seawater, a plurality of flow regulators, and a plurality of partitioned fluid passages provided in the chamber to allow the concentrated seawater port and the seawater port to communicate with each other.