A blood purification apparatus comprising: a blood circuit including an arterial blood circuit and a venous blood circuit for extracorporeally circulating blood of a patient from a tip end (a) of the arterial blood circuit to a tip end (b) of the venous blood circuit; a blood purification means arranged between the arterial blood circuit and the venous blood circuit of the blood circuit and purifying blood flowing through the blood circuit; a substitution solution supplying means (7, Lc) for supplying substitution solution to the blood circuit; and performing blood-return by substituting the blood in the blood circuit with the substitution solution supplied from the substitution solution supplying means (7, Lc) after the blood purification treatment wherein the blood purification apparatus further comprises; a detecting means (13, 14) arranged at predetermined positions in the arterial blood circuit and the venous blood circuit and detecting presence or absence or blood concentration of the blood flowing in the arterial blood circuit and the venous blood circuit at said predetermined positions, and a recognition means for recognize a final stage of blood-return which is a condition near the end of the substitution of blood with the substitution solution based on the presence or absence of the blood or blood concentration detected by the detecting means (13, 14), wherein the blood purification apparatus further comprises a control means for performing predetermined controls concerning to actions or operations carried out at the final stage of blood-return subject to the recognition of the final stage of blood-return by the recognition means, characterized in that the blood purification apparatus further comprises a monitoring means for monitoring abnormalities during the blood-return, and wherein the control means can make the abnormality monitoring by the monitoring means severe subject to the recognition of the final stage of blood-return by the recognition means. a blood circuit including an arterial blood circuit and a venous blood circuit for extracorporeally circulating blood of a patient from a tip end (a) of the arterial blood circuit to a tip end (b) of the venous blood circuit; a blood purification means arranged between the arterial blood circuit and the venous blood circuit of the blood circuit and purifying blood flowing through the blood circuit; a substitution solution supplying means (7, Lc) for supplying substitution solution to the blood circuit; and performing blood-return by substituting the blood in the blood circuit with the substitution solution supplied from the substitution solution supplying means (7, Lc) after the blood purification treatment wherein the blood purification apparatus further comprises; a detecting means (13, 14) arranged at predetermined positions in the arterial blood circuit and the venous blood circuit and detecting presence or absence or blood concentration of the blood flowing in the arterial blood circuit and the venous blood circuit at said predetermined positions, and a recognition means for recognize a final stage of blood-return which is a condition near the end of the substitution of blood with the substitution solution based on the presence or absence of the blood or blood concentration detected by the detecting means (13, 14), wherein the blood purification apparatus further comprises a control means for performing predetermined controls concerning to actions or operations carried out at the final stage of blood-return subject to the recognition of the final stage of blood-return by the recognition means, characterized in that the blood purification apparatus further comprises a monitoring means for monitoring abnormalities during the blood-return, and wherein the control means can make the abnormality monitoring by the monitoring means severe subject to the recognition of the final stage of blood-return by the recognition means.