An anti-HB-EGF antibody having an internalizing activity is disclosed. A cytotoxic substance is preferably bound to the anti-HB-EGF antibody of the present invention. Also provided are an anti-cancer agent and a cell proliferation inhibitor, which comprise the antibody of the present invention as an active ingredient, a method of treating cancer and a method of diagnosing cancer, which comprise the administration of the antibody of the present invention. Cancers that can be treated by the anti-cancer agent of the present invention include pancreatic cancer, liver cancer, esophageal cancer, melanoma, colorectal cancer, gastric cancer, ovarian cancer, uterine cervical cancer, breast cancer, bladder cancer, brain tumors, and hematological cancers.