Provided is a blood filter that contains a porous element and a copolymer, which is present on at least a part of the surface of the porous element and which contains a repeating unit containing an organic group represented by formula (a) and a repeating unit containing an organic group represented by formula (b) (in the formulae, Ua1, Ua2, Ub1, Ub2, Ub3 and An- are as set forth in the description and the claims).
