Disclosed is use of an antibody, which targets an identified cancer antigen protein specifically expressed on the surface of cancer cells, as a therapeutic and/or prophylactic agent for cancer. Specifically disclosed is a medicinal composition for treating and/or preventing cancer characterized by containing, as the active ingredient, an antibody, which comprises a heavy chain variable region comprising SEQ ID NOS:39, 40 and 41 and a light chain variable region comprising SEQ ID NOS:43, 44 and 45 and is immunologically reactive with CAPRIN-1 protein, or a fragment of said antibody.
