A blood purification apparatus comprising: a blood circuit including an arterial blood circuit and a venous blood circuit and through which blood of a patient is allowed to extracorporeally circulate; a blood purifier connected to the blood circuit and that is capable of purifying the blood extracorporeally circulating through the blood circuit; a dialysate introduction line supplied with a predetermined liquid from a liquid-feeding device and through which a dialysate is introduced into the blood purifier, the liquid-feeding device being capable of feeding the liquid at a constant pressure; a dialysate drain line through which waste water is discharged from the blood purifier; a substitution line one end of which is connected to a collecting port provided at a predetermined position of the dialysate introduction line and an other end of which is connected to the arterial blood circuit or the venous blood circuit; a closing device provided to the substitution line and that is capable of arbitrarily closing a flow route provided by the substitution line, the closing device being configured to form, in a state where the flow route is closed, a pressure-increasing portion that includes the collecting port; and a pressure-measuring device (Pc) capable of measuring a pressure in the pressure-increasing portion, the blood purification apparatus performing a testing process in which connection of the substitution line to the collecting port is checked by increasing a liquid pressure in the pressure-increasing portion and measuring the pressure with the pressure-measuring device (Pc), wherein the testing process is performed by increasing the liquid pressure in the pressure-increasing portion by utilizing a liquid-feeding pressure applied from the liquid-feeding device. a blood circuit including an arterial blood circuit and a venous blood circuit and through which blood of a patient is allowed to extracorporeally circulate; a blood purifier connected to the blood circuit and that is capable of purifying the blood extracorporeally circulating through the blood circuit; a dialysate introduction line supplied with a predetermined liquid from a liquid-feeding device and through which a dialysate is introduced into the blood purifier, the liquid-feeding device being capable of feeding the liquid at a constant pressure; a dialysate drain line through which waste water is discharged from the blood purifier; a substitution line one end of which is connected to a collecting port provided at a predetermined position of the dialysate introduction line and an other end of which is connected to the arterial blood circuit or the venous blood circuit; a closing device provided to the substitution line and that is capable of arbitrarily closing a flow route provided by the substitution line, the closing device being configured to form, in a state where the flow route is closed, a pressure-increasing portion that includes the collecting port; and a pressure-measuring device (Pc) capable of measuring a pressure in the pressure-increasing portion, the blood purification apparatus performing a testing process in which connection of the substitution line to the collecting port is checked by increasing a liquid pressure in the pressure-increasing portion and measuring the pressure with the pressure-measuring device (Pc), wherein the testing process is performed by increasing the liquid pressure in the pressure-increasing portion by utilizing a liquid-feeding pressure applied from the liquid-feeding device.