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 filtering surface on a side of the inlet space, a filtering surface on a side of the outlet space, and an end surface along peripheries of the pair of filtering surfaces, the inlet-side container element and the outlet-side container element are provided with a gripper that clamps and compresses an outer edge portion of the pair of filtering surfaces, and a thickness of the filter element is compressed at the gripper to be 0.05 to 0.5 times the thickness.