PROBLEM TO BE SOLVED: To provide a blood purification device capable of suppressing an increase in the amount of blood extracorporeally circulated during treatment while facilitating priming work. A blood circuit 2 for extracorporeally circulating a patient's blood, a blood purifier 3 provided in the blood circuit 2, and a blood circuit 2 provided downstream of the blood purifier 3 in the blood flow, The liquid level adjusting unit 6 includes a gas-liquid separator 24 that separates bubbles contained in the inflowing blood, and a liquid level adjusting unit 6 that can adjust the liquid level in the gas-liquid separator 24. The liquid level during priming is controlled to be higher than the liquid level inside. [Selection diagram] Figure 1【課題】プライミングの作業を容易としつつも、治療時に体外循環される血液量の増加を抑制可能な血液浄化装置する。【解決手段】患者の血液を体外循環させる血液回路２と、血液回路２に設けられた血液浄化器３と、血液浄化器３よりも血液の流れにおける下流側の前記血液回路２に設けられ、流入した血液に含まれる気泡を分離する気液分離器２４と、気液分離器２４内の液面高さを調整可能な液面調整部６と、を備え、液面調整部６は、治療中の液面高さよりも、プライミング時の液面高さを高く制御する。【選択図】図１
