A blood processing filter for removing undesirable components from liquid containing a blood component or blood, comprises a sheet-shaped filter element and a hard container that includes an inlet-side container element and an outlet-side container element that are disposed to clamp the filter element, and has an internal space separated by the filter element into an inlet space and an outlet space, wherein the filter element includes a pair of filtering surfaces disposed on the inlet space side and the outlet space side, the inlet-side container element and the outlet-side container element are provided with a gripper that clamps and compresses outer edge portions of the pair of filtering surfaces, the filter element is compressed to have a thickness of a portion clamped by the gripper being 0.05 times or more and 0.5 times or less larger, and the hard container is provided with a steam-permeable portion having steam permeability.
