An object of the present invention is to prepare an antibody that targets CAPRIN-1 specifically expressed on the surface of cancer cells and is superior in antitumor activity to conventional antibodies and to provide use of the antibody as a therapeutic and/or preventive agent for cancer. The present invention provides use of an antibody targeting an identified cancer antigenic protein specifically expressed on the surface of cancer cells as a therapeutic and/or preventive agent for cancer, specifically, a pharmaceutical composition for treatment and/or prevention of cancer, comprising as an active ingredient an antibody or a fragment thereof which has immunological reactivity with a CAPRIN-1 protein, the antibody or the fragment thereof comprising a heavy chain variable region comprising amino acid sequences represented by SEQ ID NOs: 5, 6, and 7 and a light chain variable region comprising amino acid sequences represented by SEQ ID NOs: 9, 10, and 11.
