A blood purification apparatus that includes a blood circuit including an arterial blood circuit and a venous blood circuit and that allows a patient's blood to extracorporeally circulate from a distal end of the arterial blood circuit to a distal end of the venous blood circuit; a blood purifier provided between the arterial blood circuit and the venous blood circuit and that is configured to purify the blood flowing through the blood circuit, the blood purifier having a blood flow route through which the blood extracorporeally circulating through the blood circuit is allowed to flow and a dialysate flow route through which dialysate is allowed to flow, the blood flow route and the dialysate flow route being separated from each other by a blood purification membrane for purifying the blood; an ultrafiltration unit that is configured to perform ultrafiltration by filtering out water from the blood in the blood flow route through the blood purification membrane and draining the water through the dialysate flow route; and a substitution-fluid supply unit that is configured to supply substitution fluid into the blood circuit, the blood purification apparatus comprising: a plasma-flow-rate-acquiring unit that is configured to acquire a plasma flow rate or a correlation value of plasma flow rate with reference to a blood concentration detected from the patient's blood and a plasma total protein detected from the blood flowing through the blood circuit, characterized in that the blood purification apparatus further comprises a substitution-rate-acquiring unit configured to calculate a substitution rate to be achieved by the substitution-fluid supply unit with reference to the plasma flow rate or the correlation value of plasma flow rate acquired by the plasma-flow-rate-acquiring unit. a blood circuit including an arterial blood circuit and a venous blood circuit and that allows a patient's blood to extracorporeally circulate from a distal end of the arterial blood circuit to a distal end of the venous blood circuit; a blood purifier provided between the arterial blood circuit and the venous blood circuit and that is configured to purify the blood flowing through the blood circuit, the blood purifier having a blood flow route through which the blood extracorporeally circulating through the blood circuit is allowed to flow and a dialysate flow route through which dialysate is allowed to flow, the blood flow route and the dialysate flow route being separated from each other by a blood purification membrane for purifying the blood; an ultrafiltration unit that is configured to perform ultrafiltration by filtering out water from the blood in the blood flow route through the blood purification membrane and draining the water through the dialysate flow route; and a substitution-fluid supply unit that is configured to supply substitution fluid into the blood circuit, the blood purification apparatus comprising: a plasma-flow-rate-acquiring unit that is configured to acquire a plasma flow rate or a correlation value of plasma flow rate with reference to a blood concentration detected from the patient's blood and a plasma total protein detected from the blood flowing through the blood circuit, characterized in that the blood purification apparatus further comprises a substitution-rate-acquiring unit configured to calculate a substitution rate to be achieved by the substitution-fluid supply unit with reference to the plasma flow rate or the correlation value of plasma flow rate acquired by the plasma-flow-rate-acquiring unit. a plasma-flow-rate-acquiring unit that is configured to acquire a plasma flow rate or a correlation value of plasma flow rate with reference to a blood concentration detected from the patient's blood and a plasma total protein detected from the blood flowing through the blood circuit, characterized in that the blood purification apparatus further comprises a substitution-rate-acquiring unit configured to calculate a substitution rate to be achieved by the substitution-fluid supply unit with reference to the plasma flow rate or the correlation value of plasma flow rate acquired by the plasma-flow-rate-acquiring unit.