An energy recovery apparatus which is used in a seawater desalination system includes a cylindrical chamber (CH) being installed such that a longitudinal direction of the chamber is placed in a vertical direction, a concentrated seawater port (P1) for supplying and discharging the concentrated seawater, a seawater port (P2) for supplying and discharging the seawater, a flow resistor (23) provided at a concentrated seawater port (P1) side in the chamber (CH), and a flow resistor (23) provided at a seawater port (P2) side in the chamber (CH). The flow resistor (23) provided at the concentrated seawater port (P1) side and the flow resistor (23) provided at the seawater port (P2) side comprise at least one perforated circular plate, and the perforated circular plate has holes formed at an outer circumferential area outside a predetermined diameter of the circular plate.