Abstract: An extracorporeal circulation apparatus capable of maintaining hypothermia for a prolonged period when used in the selective cooling method. The extracorporeal circulation apparatus used in the selective cooling method includes (1) a diluent supply unit for cooling a diluent and metering the diluent into a blood vessel; (2) a blood concentration unit for metering a diluted blood out from a blood vessel and concentrating the diluted blood thus drawn out by filtering the diluted blood; and (3) a blood supply unit for heating the concentrated blood and metering the concentrated blood into a blood vessel, wherein a flow rate of the injected diluent flow rate, Vd and a flow rate of a filtrate, Vb are so controlled that a relationship 0.1 Vd≦Vb≦Vd is maintained.