The present teachings relate to a blood purification apparatus in which the connection of a substitution line to a collecting port can be checked accurately and instantly and even during blood purification treatment. A blood purification apparatus includes a blood circuit, a dialyzer, a dialysate introduction line, a dialysate drain line, 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 blood circuit, a substitution pump configured to form a pressure-increasing portion that includes the collecting port, and a pressure-measuring device capable of measuring a pressure in the pressure-increasing portion. The blood purification apparatus performs a testing process by increasing a liquid pressure in the pressure-increasing portion by utilizing a liquid-feeding pressure applied from a liquid-feeding device and measuring the pressure with the pressure-measuring device.