It is intended to provide a CAPRIN-1-targeting antibody superior in antitumor activity to conventional antibodies, and use thereof as a therapeutic and/or preventive agent for a cancer. The present invention provides an antibody targeting a CAPRIN-1 polypeptide specifically expressed on the surface of cancer cells, and use of the antibody as a therapeutic and/or preventive agent for a cancer. The present invention provides an antibody which comprises a heavy chain variable region comprising complementarity-determining regions of SEQ ID NOs: 1, 2, and 3 and a light chain variable region comprising complementarity-determining regions of SEQ ID NOs: 4, 5, and 6 and has immunological reactivity with a CAPRIN-1 protein, or a fragment thereof, and a pharmaceutical composition for the treatment and/or prevention of a cancer, comprising this antibody or fragment as an active ingredient.
