To provide an emergency condenser capable of effectively cooling a nuclear reactor for a long time even when a cooling pump does not function due to the loss of power source.

The emergency condenser has multiple emergency water tanks each of which is equipped with a buffer tank. A gas-phase part of each emergency water tank and a gas-phase part of each buffer tank are connected by a gas-phase part pipe. The gas-phase parts of the emergency water tanks are connected by a connection pipe among each other. Liquid-phase parts of at least two emergency water tanks connected by the connection pipe between each other are configured to be connected, through respective liquid-phase part cross pipes to liquid-phase parts of the buffer tanks whose gas-phase parts are not connected by the gas-phase part pipe. By using a pressure difference between the two emergency water tanks, water in the buffer tank is supplied to the emergency water tank via the liquid-phase part cross pipe.