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; a blood purification device that is connected between the arterial blood circuit and the venous blood circuit, and that purifies the blood which flows through the blood circuit; a dialysate introduction line that introduces dialysate into the blood purification device and a dialysate discharge line that discharges dialysate from the blood purification device; a pressure detection device (α to γ) that is configured to detect a pressure in the dialysate introduction line or the dialysate discharge line, or a pressure in the blood circuit; a dialysate extraction device which is connected to the dialysate introduction line, and in which an extraction port through which the flowing dialysate is extractable is formed; a dialysate supply line (La) with one end connected to the extraction port of the dialysate extraction device and the other end connected to the blood circuit, the dialysate supply line (La) is configured to supply the dialysate of the dialysate introduction line to the blood circuit; and a check valve that is connected to the dialysate extraction device or the dialysate supply line (La), that allows a flow of liquid from the dialysate introduction line to the blood circuit and blocks a flow of liquid from the blood circuit to the dialysate introduction line, wherein the blood purification apparatus includes a control means that is configured to generate a pressure difference across the check valve with a side of the blood circuit higher in pressure than a side of the dialysate introduction line, a monitor means that is configured to monitor a change in a detection value of the pressure detection device (α to γ) based on the pressure difference, and a determination means that is configured to determine whether or not blocking of liquid by the check valve is appropriate based on the change in the detection value of the pressure detection device (α to γ). a blood circuit including an arterial blood circuit and a venous blood circuit for extracorporeally circulating blood of a patient; a blood purification device that is connected between the arterial blood circuit and the venous blood circuit, and that purifies the blood which flows through the blood circuit; a dialysate introduction line that introduces dialysate into the blood purification device and a dialysate discharge line that discharges dialysate from the blood purification device; a pressure detection device (α to γ) that is configured to detect a pressure in the dialysate introduction line or the dialysate discharge line, or a pressure in the blood circuit; a dialysate extraction device which is connected to the dialysate introduction line, and in which an extraction port through which the flowing dialysate is extractable is formed; a dialysate supply line (La) with one end connected to the extraction port of the dialysate extraction device and the other end connected to the blood circuit, the dialysate supply line (La) is configured to supply the dialysate of the dialysate introduction line to the blood circuit; and a check valve that is connected to the dialysate extraction device or the dialysate supply line (La), that allows a flow of liquid from the dialysate introduction line to the blood circuit and blocks a flow of liquid from the blood circuit to the dialysate introduction line, wherein the blood purification apparatus includes a control means that is configured to generate a pressure difference across the check valve with a side of the blood circuit higher in pressure than a side of the dialysate introduction line, a monitor means that is configured to monitor a change in a detection value of the pressure detection device (α to γ) based on the pressure difference, and a determination means that is configured to determine whether or not blocking of liquid by the check valve is appropriate based on the change in the detection value of the pressure detection device (α to γ).