PROBLEM TO BE SOLVED: To provide a priming method of a blood treatment filter device for performing priming easily and reliably.SOLUTION: In a priming method, parts between connection positions 35 and 36 of a first bypass circuit 33 and connection positions 37 and 38 of a second bypass circuit 34 are respectively blocked in a first blood circuit 31 and a second blood circuit 32. A liquid for priming flows into an inner space of a body container 21 from a second port 23 through the first bypass circuit 33 and the second blood circuit 32 from the first blood circuit 31, and the liquid for priming flows out from the inner space of the body container 21 to the second blood circuit 32 through the first blood circuit 31 and the second bypass circuit 34 from a first port 22.
