The purpose of the present invention is to provide a blood purification device that can surely prevent extracorporeal circulation of the blood of a patient in a blood circuit when a puncture needle incorrectly punctures an access blood vessel.The blood purification device according to the present invention, which comprises a blood circuit (1) for extracorporeally circulating the blood of a patient and a dialyzer (2) for purifying the blood flowing through the blood circuit (1), is equipped with: a pressure change-applying means capable of applying a positive pressure or a negative pressure to a front end of the blood circuit (1) in a state where an arterial side puncture needle (a) and a venous side puncture needle (b) are not connected in the blood purification device； a pressure change-detecting means capable of detecting a pressure change at the front end of the blood circuit (1), when the front end of the blood circuit (1), to which the positive pressure or negative pressure is applied by the pressure change-applying means, is connected to the arterial side puncture needle (a) and the venous side puncture needle (b), both puncture needles puncturing the patient's body； and a determination means (11) capable of determining whether or not the arterial side puncture needle (a) and the venous side puncture needle (b) normally puncture on the basis of the pressure change detected by the pressure change-detecting means.La présente invention vise à fournir un dispositif de purification de sang qui peut empêcher de façon sûre la circulation extracorporelle du sang d'un patient dans un circuit de sang lorsqu'une aiguille de perforation perfore un vaisseau sanguin d'accès de façon inappropriée. Le dispositif de purification de sang, selon la présente invention, qui a un circuit de sang (1) pour la circulation extracorporelle du sang d'un patient et un dialyseur (2) pour purifier le sang s'écoulant à travers le circuit de sang (1), comprend : un moyen d'application de ch
