The present inventors succeeded in producing an anti-Epiregulin antibody that exhibits a species crossreactivity between a non-human animal crab-eating monkey and a human animal, an anti-Epiregulin antibody that rarely undergoes chemical decomposition, an anti-Epiregulin antibody that has a decreased isoelectric point, an anti-Epiregulin antibody that has an elevated thermal denaturation midpoint temperature and an anti-Epiregulin antibody that is reduced in the amount of aggregates, by properly substituting an amino acid residue in the sequence for a variable region of a humanized EP27 antibody that can exhibit a cytotoxic activity and a neutralization activity on an anti-human Epiregulin-expressing cancer cell (i.e., a cancer cell that exhibits an anti-human Epiregulin) to thereby inhibit the proliferation of the cancer cell.
