An energy recovery device is provided in a seawater desalination system for desalinating seawater by removing salinity from the seawater. A pressure exchange chamber for pressurizing seawater by a pressure of concentrated seawater discharged from a reverse-osmosis membrane-separation apparatus includes a first supply and discharge port connected to a switching valve for performing supply and discharge of liquid, a second supply and discharge port connected to a directional control valve for performing supply and discharge of liquid, a flow resistor provided at the first supply and discharge port side in the chamber and configured to regulate the flow, and a flow resistor provided at the second supply and discharge port side in the chamber and configured to regulate the flow, and a flowmeter provided between the two flow resistors and configured to measure a flow rate of the liquid in the chamber.