Abstract: A blood reservoir, commonly used in a blood circuit with an artificial lung, includes a blood extraction line chamber provided inside a housing and having a blood extraction line connection port, the chamber temporarily accommodating blood from a vena cava received via the connection port, a suction line chamber provided inside the housing and having a suction line connection port, the chamber temporarily accommodating blood, drawn in during open-heart surgery, received via the connection port, a blood pooling chamber provided inside the housing and communicating with the blood extraction line chamber and the suction line chamber for pooling blood accommodated by the two chambers, filtering/defoaming member arranged to communicate the suction line and blood pooling chambers for filtering and defoaming blood accommodated in the suction line chamber, an extracted blood inflow tube having one end communicating with the blood extraction line connection port and another end open to the blood extraction line chambe