The purpose of the present invention is to provide a blood purifying system whereby troublesome preparatory works for the operation of the system can be avoided and the burden on an operator can be reduced while protecting the patient s security. The blood purifying system (80) comprises: a blood pump (81) for feeding blood on an artery side circuit toward a blood purifier a dialysate pump (82) for feeding dialysate on a dialysate circuit toward the blood purifier a liquid waste pump (83) for feeding out liquid waste on a liquid waste circuit a first pump (84) for feeding a replenishing liquid on a first circuit toward a vein side circuit a second pump (85) for feeding a displacement liquid on a second circuit toward the vein side circuit and a control unit (90) for controlling the drive of these pumps. The control unit (90) controls the flow rate of the first pump (84) in conjunction with the flow rate of the second pump (85).
