PROBLEM TO BE SOLVED: To provide an autotransfusion method hardly returning protein that has clogged a dialyzer membrane, into blood to have a less amount of recovery in autotransfusion, and to provide a blood purifying apparatus that allows such the autotransfusion.SOLUTION: The blood purifying apparatus includes: a blood purifier 1 a blood circuit 2 a blood pump 3 provided in an artery side blood circuit 21 a vein chamber 23 provided in a vein side blood circuit 22 and a dialysate circuit 4. The dialysate circuit 4 includes a viscous chamber 6 to which closed water removal control can be performed. An air lead-in unit 5 is provided in the dialysate circuit 4 on the blood purifier 1 side rather than the viscous chamber 6. The air lead-in unit 5 includes a dialysate discharge line 51 provided in a dialysate supply circuit 41, and an air lead-in line 52 provided in a drainage circuit 42, and a dialysate flows upward from the lower side of the blood purifier 1. The air lead-in line 52 includes an air filter 521 at an air lead-in port.
