PROBLEM TO BE SOLVED: To provide a blood treatment filter that can increase the amount of treatment per unit time and per unit area by preventing impediment of flow and degradation of filtration performance caused by adhesion or the like between an exit side container and a filter member.SOLUTION: The blood treatment filter 1 includes the sheet-like filter member 5 disposed so as to partition both sides in the flexible container 2. The filter includes: a blood inlet opening 3a that is provided in one side of the flexible container 2 and blood outlet openings 4a, 4b that are provided in the other side of the flexible container 2. Single inlet opening 3a is provided, and a plurality of the outlet openings 4a, 4b are provided.
