PROBLEM TO BE SOLVED: To provide a blood storage tank capable of preventing a high impact positive pressure applied to an introduction port for a blood replacement fluid, the high impact positive pressure being caused from an inflow pressure of venous blood.SOLUTION: A blood storage tank includes a chamber, a venous blood inflow port to let venous blood removed from a vein of a patient flow into a chamber, a venous blood filtration unit 30 to filtrate the venous blood flowed into the venous blood inflow port, and a blood replacement fluid introduction port for introducing a blood replacement fluid into the chamber. In an internal space of the venous blood filtration unit 30, a venous blood inflow tube 23 connected at one end to the venous blood inflow port and opened at the other end, and a blood replacement fluid introduction tube 24 connected at one end to the blood replacement fluid introduction port and opened at the other end are disposed in a vertical direction. An opening area of an opened end 24a that is the other opened end of the blood replacement fluid introduction tube 24 is greater than a cross-sectional area of a flow path perpendicular to an extending direction of the blood replacement fluid introduction tube 24.SELECTED DRAWING: Figure 6
