The blood bag system (30) includes: a blood treating filter (8) for treating a blood a first bag (1) for containing therein a blood to be supplied to the blood treating filter (8) a second bag (2) for containing therein the blood treated by the blood treating filter (8) storage solution supply means (7) for supplying a blood component storage solution to the blood treating filter (8) a third bag (3) into which a blood remaining in the blood treating filter (8) replaced by the blood component storage solution is transferred and in which the recovered blood is temporarily contained and a fourth bag (4) to which a blood component separated from the treated blood contained in the second bag (2) is transferred and in which the thus transferred blood component is contained.
