A filter for processing blood that comprises a flexible container having an inlet and an outlet for blood, and a sheet-like blood processing filter material situated in such a manner so as to partition the inside of the container into an inlet side and an outlet side, wherein the flexible container comprises a container body which houses the blood processing filter material and an outlet port that forms the outlet, and the outlet port has a protrusion that protrudes from the container body into the inside of the container body, the protrusion having a plurality of fluid channel inlets formed at locations that are not in contact with the blood processing filter material.
