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