PROBLEM TO BE SOLVED: To provide a useful blood processing filter which can fully easily and surely discharge air in a collection bag for storing blood after filtration.SOLUTION: The blood processing filter includes: a sheet-like filter material a container which is jointed to flexible sheets storing the sheet-like filter material a first joint part for defining a blood processing region by jointing the filter material and the container a second joint part for jointing the periphery of the container an entrance installed in one side of the container and an exit installed in the other side of the container. The first joint part includes: an entrance side joint part for jointing faces of the flexible sheets of the entrance side of the container and the entrance side of the filter material and an exit side joint part for jointing faces of the flexible sheets of the exit side of the container and the exit side of the filter material. Peel strength of the exit side joint part is lower than that of the entrance side joint part so that the flexible sheets can be peelable from the face of the exit side of the filter material in the exit side joint part by pulling the flexible sheets composed of the exit side of the container.
