A blood purification apparatus that includes a blood circuit including an arterial blood circuit provided with an arterial puncture needle and a venous blood circuit provided with a venous puncture needle with which an access vessel is puncturable, the blood circuit allowing blood of the patient to extracorporeally circulate; a blood purifier connected to the arterial blood circuit and to the venous blood circuit and that purifies the blood flowing through the blood circuit; a blood pump provided to the arterial blood circuit; a recirculating-blood-detecting unit capable of detecting recirculating blood when the blood of the patient is caused to extracorporeally circulate through the blood circuit by activating the blood pump, the recirculating blood being blood once returned to the patient from the venous blood circuit and reintroduced into the arterial blood circuit; and a recirculation-rate-calculating unit capable of calculating recirculation rate, the recirculation rate being a proportion of the recirculating blood in the blood flowing in the arterial blood circuit. The blood purification apparatus includes a control unit capable of executing a treatment mode in which blood purification treatment is performed with the blood purifier while the blood of the patient is caused to extracorporeally circulate through the blood circuit by activating the blood pump in a state of normal connection where an upstream part of the access vessel is punctured with the puncture needle at a distal end of the arterial blood circuit and a downstream part of the access vessel is punctured with the puncture needle at a distal end of the venous blood circuit; and a measurement mode in which the detection of recirculating blood by the recirculating-blood-detecting unit and the calculation of recirculation rate by the recirculation-rate-calculating unit are performed while the blood of the patient is caused to extracorporeally circulate through the blood circuit by activating the blood pump in a state of reverse connection where the downstream part of the access vessel is punctured with the puncture needle at the distal end of the arterial blood circuit and the upstream part of the access vessel is punctured with the puncture needle at the distal end of the venous blood circuit, the calculated recirculation rate being used in calculating blood flow rate in the access vessel that is calculable in the measurement mode.