Provided is a filler for affinity chromatography having a high dynamic binding capacity for proteins and having excellent alkali resistance and storage stability. The filler for affinity chromatography of the present invention comprises a porous particle consisting of a copolymer of 40 parts to 99.5 parts by mass of (M-1) a methacryloyl group-containing vinyl monomer that contains a hydroxyl group and does not contain an epoxy group, 0.5 parts to 30 parts by mass of (M-2) an epoxy group-containing vinyl monomer, 0 parts to 59.5 parts by mass of (M-3) a methacryloyl group-containing vinyl monomer which is other than the monomers (M-1) and (M-2), and 0 parts to 25 parts by mass of (M-4) a vinyl monomer other than the monomers (M-1), (M-2) and (M-3) (with the proviso that the total amount of the contents of (M-1), (M-2), (M-3) and (M-4) is 100 parts by mass); ring-opened epoxy group obtainable by ring-opening of epoxy group that is contained in the copolymer; and ligand that is bound to the porous particle.