Abstract: A blood purification apparatus has a blood circuit, a blood pump and a blood purification instrument. A dialysate is introduced into and exits the blood purifying instrument. The blood purification apparatus has a pressure varying mechanism to vary pressure in a closed circuit under a condition where the blood circuit is formed as a closed circuit in a sealed condition connecting the tip end of the arterial blood circuit and the tip end of the venous blood circuit. A liquid leakage detecting mechanism detects liquid leakage in the blood circuit in accordance with pressure variation generated by the pressure varying mechanism.

Abstract: A blood purification apparatus has a dialyzer (1), an arterial blood circuit (2) with a blood pump 4, a venous blood circuit 3, a dialysate introduction line L1, a dialysate discharge line L2, a substitution line L3, and a substitution pump 9 that supplies the dialysate flowing in the substitution line L3 to the arterial blood circuit 2. A control device (11) estimates or measures the concentration of blood in a dilution channel section A. The control device (11) controls the volume of dialysate supplied by the substitution pump 9 on the basis of the estimated or measured blood concentration.