This is to provide a blood filter comprising a porous element； and a copolymer which exists in at least a part of a surface of the porous element, and which contains a recurring unit containing an organic group of the following formula (a) and a recurring unit containing an organic group of the following formula (b), wherein U a1 , U a2 , U b1 , U b2 and U b3 , and An - are as defined in the present specification and the claims.
