To remarkably reduce costs by circulating a dialytic liquid, performing dialysis in the state of counterflow with distilled water or RO water and providing the state of enabling connection with a patient by dialyzing the distilled water or RO water and making isotonic with a body fluid.

By starting a blood pump 10, distilled water or RO water collected in an artery side blood circuit 3, vein side blood circuit 4 and dialyzer 2 is circulated in the direction of the artery side blood circuit 3, dialyzer 2 and vein side blood circuit 4. On the other hand, the pump of a patient monitoring device 5 is started, and a dialytic liquid 6 is circulated in the direction of an outlet line 7, dialyzer 2 and inlet line 8 and contacted with distilled water or RO water in the state of counterflow. Then, distilled water or RO water inside the dialyzer 2 and the blood circuits 3 and 4 gets isotonic with distilled water or dialytic liquid inside the dialyzer 2 after the lapse of prescribed time and turned into the same state as collecting a physiological saline solution in the artery side blood circuit 3, vein side blood circuit 4 and dialyzer 2 from the biginning.