A blood purification apparatus has a dialyzer (1), an arterial blood circuit (2) with a blood pump (4), a venous blood circuit (3), a dialysis fluid introduction line (L1), a dialysis fluid discharge line (L2), a dialysate infusing line (L8), and a dialysate infusing pump (13). A closed circuit is formed in the flow route of the dialysis fluid on the dialysis fluid introduction line (L1) side including a predetermined part where a collection port (11) is formed. A testing process is performed to confirm the connection of the dialysate infusing line (L8) to the collection port (11) by measuring fluid pressure within the closed circuit while driving the dialysate infusing pump (13).