[PROBLEMS] To provide a blood purification device comprising a pressure measurement chamber which can suppress a change in a liquid level to measure the pressure of blood with higher accuracy. [MEANS FOR SOLVING PROBLEMS] A blood purification device comprising a blood circuit (1), a blood pump (3), a dialyzer (2) for purifying blood which flows through the blood circuit (1), a pressure measurement chamber (4) for measuring the pressure of blood which flows through the blood circuit (1), and a drip chamber (5) for removing bubbles from the blood which flows through the blood circuit (1). The pressure measurement chamber (4) is formed on the lower part in a storage space (4a) and comprises a blood introduction part (4b), which is open at a part near the bottom of the storage space (4a), for introducing blood, and a blood lead-out part (4c) for leading out the blood introduced through the blood introduction part (4b). The blood lead-out part (4c) extends toward the blood introduction part (4b) to a position, where the opening of the blood lead-out part (4c) faces the opening of the blood introduction part (4b) while providing a clearance of a very small size t, and the opening of the blood lead-out part (4c) covers substantially the whole area of the opening of the blood introduction part (4b).
