PROBLEM TO BE SOLVED: To provide a blood purifying device allowing leakage of blood to a branch line to be surely recognized, and allowing such an abnormal state that the blood infiltrates the branch line to be recognized in an early stage.SOLUTION: A blood purifying device includes: a blood circuit formed of an arterial blood circuit 1 and a venous blood circuit 2 and capable of extracorporeally circulating the blood of a patient from a distal end of the arterial blood circuit 1 to a distal end of the venous blood circuit 2 a dialyzer 3 which is interposed between the arterial blood circuit 1 and the venous blood circuit 2 of the blood circuit and purifies the blood flowing through the blood circuit and branch lines (L3, L4, L5, L6) which are connected to a prescribed part of the blood circuit at the distal end, communicated with the blood circuit and extended. The blood purifying device further includes blood discriminators (13, 15, 17, 19) capable of detecting that the blood extracorporeally circulated in the blood circuit has infiltrated the branch line.
