PROBLEM TO BE SOLVED: To reliably transfer treated blood in a blood line to a recovery bag by introducing gas in a gas container to a space in an outflow side liquid chamber even when the treated blood remains in the blood line.SOLUTION: A blood circuit includes a filtration unit 42 which removes a predetermined blood component from blood flowing in a blood line extending in a vertical direction and passes the blood as treated blood 91. The filtration unit 42 includes: a housing 58 having a flow inlet 82, a flow outlet 84, an inflow side liquid chamber 86 and an outflow side liquid chamber 88； and a filtration material 56 which is accommodated in the housing 58 and removes a predetermined blood component from blood. The filtration unit further includes: a gas line 90 in which one end thereof communicates with the outflow side liquid chamber 88 and the other end is connected to a gas container 50； and a second sealing member 52 which is disposed on the gas line 90 and is operated to enable the gas container 50 to communicate with a space in the outflow side liquid chamber 88.【課題】処理済み血液が血液ライン中に残存していた場合でも、気体容器内の気体を流出側液室の空間に導入することで確実に血液ライン中の処理済み血液を回収バッグに移送可能とする。【解決手段】鉛直方向に沿って延びる血液ラインを流れる血液から所定の血液成分を除去して処理済み血液９１とする濾過部４２を有する血液回路において、濾過部４２は、流入口８２、流出口８４、流入側液室８６及び流出側液室８８を有するハウジング５８と、ハウジング５８に収容され、血液から所定の血液成分を除去する濾過材５６とを有する。さらに、一端が流出側液室８８と連通し、他端が気体容器５０に接続される気体ライン９０と、気体ライン９０上に設けられ、操作によって気体容器５０と流出側液室８８の空間とを連通可能とする第２封止部材５２とを有する。【選択図】図４
