A seawater desalination system which can solve a problem of wear of a sliding member and can suppress mixing of concentrated seawater and seawater by making an energy exchange chamber no-piston configuration is provided. 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 (4) to separate the seawater into fresh water and concentrated seawater, an energy exchange chamber (20) for utilizing pressure energy of the concentrated seawater discharged from the reverse-osmosis membrane-separation apparatus (3) as energy for pressurizing part of the seawater is provided. The energy exchange chamber includes a concentrated seawater port (P1) for introducing and discharging the concentrated seawater, a seawater port (P2) for introducing and discharging the seawater, and a plurality of partitioned fluid passages (R) provided in the chamber to allow the concentrated seawater port (P1) and the seawater port (P2) to communicate with each other.