An extracorporeal circulator (100A, 100B) comprising: a venous line for drawing blood from a patient; a blood pump for feeding the blood; an artificial lung that performs gas exchange of the blood; an arterial line for feeding the blood that has passed through the artificial lung to the patient; a bubble removing unit (1A, 1 B) that removes the bubbles mixed in the blood; blood-feed control means for controlling the amount of blood being fed so as not to feed the bubbles to the patient; and a bypass line for bypassing the blood discharged from the blood pump and returning the blood to the blood pump, wherein the bubble removing unit (1A, 1B) comprises: a circulation-flow forming chamber including an inner space having a substantially circular cross section; an inlet disposed substantially tangential to the inner periphery of the circulation-flow forming chamber, for introducing the blood into the circulation-flow forming chamber so that the blood forms a circulation flow in the circulation-flow forming chamber; an outlet disposed at the lower part of the circulation-flow forming chamber; and a bubble reservoir disposed on the circulation-flow forming chamber, for temporarily storing the bubbles rising from the circulation-flow forming chamber, characterized in that the bubble reservoir further comprises: a vacuum chamber disposed on the bubble reservoir and connected to deaerator means to be maintained at a negative pressure; a first filter disposed to partition the bubble reservoir and the vacuum chamber from each other and allowing the passage of gas and rejects the passage of blood; and a second filter disposed between the vacuum chamber and the deaerator means and allowing the passage of gas and rejects the passage of liquid. a venous line for drawing blood from a patient; a blood pump for feeding the blood; an artificial lung that performs gas exchange of the blood; an arterial line for feeding the blood that has passed through the artificial lung to the patient; a bubble removing unit (1A, 1 B) that removes the bubbles mixed in the blood; blood-feed control means for controlling the amount of blood being fed so as not to feed the bubbles to the patient; and a bypass line for bypassing the blood discharged from the blood pump and returning the blood to the blood pump, wherein the bubble removing unit (1A, 1B) comprises: a circulation-flow forming chamber including an inner space having a substantially circular cross section; an inlet disposed substantially tangential to the inner periphery of the circulation-flow forming chamber, for introducing the blood into the circulation-flow forming chamber so that the blood forms a circulation flow in the circulation-flow forming chamber; an outlet disposed at the lower part of the circulation-flow forming chamber; and a bubble reservoir disposed on the circulation-flow forming chamber, for temporarily storing the bubbles rising from the circulation-flow forming chamber, characterized in that a circulation-flow forming chamber including an inner space having a substantially circular cross section; an inlet disposed substantially tangential to the inner periphery of the circulation-flow forming chamber, for introducing the blood into the circulation-flow forming chamber so that the blood forms a circulation flow in the circulation-flow forming chamber; an outlet disposed at the lower part of the circulation-flow forming chamber; and a bubble reservoir disposed on the circulation-flow forming chamber, for temporarily storing the bubbles rising from the circulation-flow forming chamber, the bubble reservoir further comprises: a vacuum chamber disposed on the bubble reservoir and connected to deaerator means to be maintained at a negative pressure; a first filter disposed to partition the bubble reservoir and the vacuum chamber from each other and allowing the passage of gas and rejects the passage of blood; and a second filter disposed between the vacuum chamber and the deaerator means and allowing the passage of gas and rejects the passage of liquid. a vacuum chamber disposed on the bubble reservoir and connected to deaerator means to be maintained at a negative pressure; a first filter disposed to partition the bubble reservoir and the vacuum chamber from each other and allowing the passage of gas and rejects the passage of blood; and a second filter disposed between the vacuum chamber and the deaerator means and allowing the passage of gas and rejects the passage of liquid.