A blood treatment filter including: a filter container that introduces blood from an inlet into an internal space, and discharges treated blood from an outlet; a filter material that is housed in the filter container to partition the internal space into an inlet side space and an outlet side space, and filters the passing blood to remove a specific component; an inlet port that forms an inlet channel through which the blood flowing from the inlet to the internal space passes; an outlet port that forms an outlet channel through which the blood flowing from the internal space to the outlet passes, wherein the outlet channel has a tapered outlet passage with an inner diameter increasing from the internal space side toward the outlet side.
