[Object] To provide a blood purification apparatus which can reliably substitute blood during returning of blood and suppress a supply amount of a substitution solution.[Solution] The blood purification apparatus includes a blood circuit that is formed to have an arterial blood circuit 1 and a venous blood circuit 2 and that can extracorporeally circulate blood of a patient from a tip of the arterial blood circuit 1 to a tip of the venous blood circuit 2 and a dialyzer 3 that is interposed between the arterial blood circuit 1 and the venous blood circuit 2 and that purifies the blood. The blood purification apparatus can substitute the blood inside the blood circuit during returning of the blood after treatment. The blood purification apparatus further includes an air circulation line that is connected to a predetermined portion in the blood circuit and that can circulate air an air pump 18 that can supply the air into the blood circuit via the air circulation line and a control device 19 that controls the air pump 18 to supply the air into the blood circuit during returning of the blood.
