A blood purification apparatus that is capable of performing a liquid spill prevention operation and uniformizing the amount of air introduced through an opened portion. The blood purification apparatus includes a dialysate introduction line that allows dialysate to be introduced into a dialyzer; a dialysate discharge line that allows the dialysate to be discharged from the dialyzer; coupling tools that allow free switching between a connected state which causes a closed circuit, and an opened state which causes the closed circuit to be opened to form an opened portion; and a control means that performs a liquid spill prevention operation in which external air is introduced through the opened portion. An air detection means, by which air introduced through the opened portion is detectable, is provided in the vicinity of the coupling tools, and the control means stops the liquid spill prevention operation when air is detected by the air detection means.