To provide a blood processing system capable of strictly controlling a supply flow rate of treatment liquid to a blood processing circuit while replenishing a storage container of a blood processing device with treatment liquid during blood processing.SOLUTION: A blood purification system 1 includes: an external liquid discharge circuit 100； a gravimeter 52； and a waste liquid controller 12 that while waste liquid in a waste liquid container 50 is not discharged to the outside from the external liquid discharge circuit 100, calculates an actual flow rate of a first liquid discharge pump 51 from a variation amount of weight of the waste liquid container 50 measured by the gravimeter 52 and corrects a flow rate error between the actual flow rate and a target flow rate by controlling the first liquid discharge pump 51 and, while waste liquid in the waste liquid container 50 is discharged to the outside from the external liquid discharge circuit 100 by a second discharge pump 111, controls the first liquid discharge pump 51 using a correction value of a flow rate error immediately before starting discharge of the waste liquid. The second discharge pump 111 is actuated when an amount of waste liquid stored in the waste liquid container 50 becomes equal to or larger than a predetermined threshold and is stopped when the amount of waste liquid stored in the waste liquid container 50 becomes equal to or smaller than a predetermined amount.SELECTED DRAWING: Figure 4【課題】血液処理中に血液処理装置の貯留容器に治療液を補充しながら、血液処理回路への治療液の供給流量を厳格に制御可能な血液処理システムを提供する。【解決手段】血液浄化システム１は、外部排液回路１００と、重量計５２と、排液容器５０の排液が外部排液回路１００から外部に排出されていない間は、重量計５２により測定された排液容器５０の重量の変化量から、第１の排液ポンプ５１の実流量を算出し、第１の排液ポンプ５１を制御して実流量と目標流量との流量誤差を補正し、排液容器５０の排液が第２の排液ポンプ１１１により外部排液回路１００から外部に排出されている間は、当該排液の排出が開始される直前の流量誤差の補正値を用いて第１の排液ポンプ５１を制御する排液制御装置１２と、を有する。第２の排液ポンプ１１１は、排液容器５０に所定の閾値以上の排液が溜まった場合に作動し、排液容器５０の排液が所定量以下に減少すると停止する。【選択図】図４
