The present invention provides a blood circuit capable ofautomatically performing priming for safe treatments.The blood circuit includes: a hemofilter (56) purifying blood； ablood removal line that has an end connected to an inlet of thehemofilter (56) and that consists of a first blood removal line (84), asecond blood removal line (88), and a third blood removal line (89)； ablood return line that has an end connected to an outlet of thehemofilter (56) and that consists of the first blood return line (92) andthe second blood return line (94)； and an anticoagulant (bypass) line(90) reducing a difference between (a) a pressure of a priming fluidflowing in the blood removal line and (b) a pressure of the primingfluid flowing in the blood return line.
