The objective of the present invention is to provide an antibody that targets CAPRIN-1 and that exhibits antitumor activity superior to that of conventional antibodies, and an application for said antibody as a therapeutic agent and/or preventative agent for cancer. The present invention provides an antibody that targets CAPRIN-1 polypeptides that are specifically expressed on the surface of cancer cells, and an application for the antibody as a therapeutic agent and/or preventative agent for cancer. Provided are an antibody that is immunologically reactive with CAPRIN1-protein and a fragment of said antibody, the antibody containing a heavy chain region including the complementarity determining regions of SEQ ID Nos. 1, 2 and 3, and a light chain region including the complementarity determining regions of SEQ ID Nos. 4, 5 and 6. Further provided is a pharmaceutical composition for the treatment and/or prevention of cancer and having the antibody or fragment as an active ingredient thereof.
