It is intended to identify a cancer antigenic protein specifically expressed on the surface of cancer cells and to provide an antibody targeting the antigenic protein and use of the antibody as a therapeutic and/or preventive agent for cancer. The present invention provides an antibody or a fragment thereof which has immunological reactivity with a CAPRIN-1 protein, the antibody comprising a heavy chain variable region comprising amino acid sequences of SEQ ID NOs: 5, 6, and 7 and a light chain variable region comprising amino acid sequences of SEQ ID NOs: 9, 10, and 11, and a pharmaceutical composition for treatment and/or prevention of cancer, comprising this antibody or fragment as an active ingredient.