The present invention is a blood purification device that comprises: a blood circuit that has an artery-side blood circuit and a vein-side blood circuit and that makes the blood of a patient circulate extracorporeally from a tip end of the artery-side blood circuit to a tip end of the vein-side blood circuit； a blood purifier that is interposed between the artery-side blood circuit and the vein-side blood circuit, that purifies blood that is flowing in the blood circuit, and that has formed therein, across a blood purification membrane that is for purifying blood, a blood channel in which blood that is circulating extracorporeally in the blood circuit flows and a dialysate channel in which a dialysate flows； a water removal part that removes water by filtering water from the blood in the blood circuit via the blood purification membrane and discharging the water from the dialysate channel； and a replacement liquid supply part that supplies replacement liquid to the blood circuit. The blood purification device is characterized by comprising a plasma flow rate acquisition part that acquires a plasma flow rate or a correlation value for the plasma flow rate on the basis of a blood concentration detected from the blood of the patient and of a plasma total protein detected from the blood flowing in the blood circuit.La présente invention concerne un dispositif de purification du sang qui comprend : un circuit sanguin qui a un circuit sanguin côté artère et un circuit sanguin côté veine et qui amène le sang d'un patient à circuler de manière extracorporelle d'un embout du circuit sanguin côté artère jusqu'à un embout du circuit sanguin côté veine ； un purificateur de sang qui est interposé entre le circuit sanguin côté artère et le circuit sanguin côté veine, qui purifie le sang qui circule dans le circuit sanguin, et qui a, formés à l'intérieur, à travers une membrane de purification de sang qui est destinée à purifier le sang, un canal de sang dans lequel le sang qui ci
