Disclosed are antibodies that bind to Prominin-1 and have ADCC activity and/or CDC activity, and pharmaceutical compositions containing those antibodies. Recombinant antibodies were produced by cloning a nucleotide sequence of the AC133 antibody variable region and it was discovered that the ADCC/CDC-inducing effect which does not exist in the original AC133 antibody is imparted to the recombinant antibodies. In the human chimeric antibody/human effector cell combination, the chimeric antibody whose constant region sequence had been converted to human IgG1/κ was found to induce strong ADCC. Humanized antibodies were prepared by grafting the AC133 antibody CDRs to a human antibody sequence, producing humanized antibodies having binding activities equivalent to the activity of the chimeric antibody. Also disclosed are unlabeled AC133 human chimeric antibodies and humanized antibodies having antitumor effects.