The present invention relates to a blood purification apparatus in which the connection of a substitution line (L9) to a collecting port (11) can be checked accurately and instantly and even during blood purification treatment. A blood purification apparatus includes a blood circuit (2), a dialyzer (3), a dialysate introduction line (L1), a dialysate drain line (L2), a substitution line (L9) one end of which is connected to a collecting port (11) provided at a predetermined position of the dialysate introduction line (L1) and an other end of which is connected to the blood circuit (2), a substitution pump (13) configured to form, in a state where a flow route is closed, a pressure-increasing portion that includes the collecting port (11), and a pressure-measuring device (Pc) capable of measuring a pressure in the pressure-increasing portion. The blood purification apparatus performs a testing process in which connection of the substitution line (L9) to the collecting port (11) is checked 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 (Pc).
