Disclosed is an antibody capable of binding to Claudin-6 (CLDN6) which is expressed on the surface of a cell membrane. The antibody can recognize human CLDN6 occurring on the surface of a cell membrane in its native form, and has a cytotoxic activity (e.g., ADCC activity and a CDC activity) against a cancer cell line which expresses human CLDN6 at a high level. A conjugate of the antibody and a toxin has an inhibitory activity on the cell proliferation of a cancer cell line which expresses human CLDN6 at a high level. The expression of human CLDN6 is not observed in a normal tissue, but is increased in a tumor tissue (e.g., pulmonary adenocarcinoma, gastric cancer, ovarian cancer). The anti-CLDN6 antibody is expected to be highly accumulated in tumor in which human CLDN6 has been expressed at a high level, and therefore can be used as an extremely effective anti-tumor agent.
