[Problem]Provided is a blood purification device that can ease the burden on a medical professional and can suppress an air bubble from flowing to the tip side of an artery-side blood circuit during an artery-side blood return step. [Solution] The blood purification device is equipped with a control means (19) that can perform: a vein-side blood return step (S1) that, when returning blood, performs blood return having replaced the blood from the section of a blood circuit connecting to a physiological saline solution supply line (8) to the tip of a vein-side blood circuit (2) with a physiological saline solution an artery-side blood return step (S4) that performs blood return having replaced the blood from the section of the blood circuit connecting to the physiological saline solution supply line (8) to the tip of an artery-side blood circuit (1) with a physiological saline solution and a negative pressure application step (S1a) that, while driving a blood pump (4) in the forward direction, causes a physiological saline solution supply line (8) to go from an occluded state to a flow-through state by means of a solenoid valve (V3), applies negative pressure to the flow path on the upstream side of the position of installation of the blood pump (4) in the artery-side blood circuit (1), and then releases the negative pressure.Pour obtenir un dispositif de purification du sang qui peut alléger le fardeau dun professionnel de santé et empêcher une bulle dair de sécouler vers lextrémité dun circuit de circulation du sang côté artère, au cours dune étape de retour du sang côté artère, la solution suivante est proposée. Le dispositif de purification du sang est équipé pour cela dun moyen de commande (19) qui peut réaliser : une étape de retour du sang côté veine (S1) qui, lors du retour du sang, permet de renvoyer le sang ayant remplacé celui provenant de la section dun circuit de circulation du sang raccordant une ligne dalimentation (8) de solution saline physiologique à
