According to the present invention, an anticancer agent is provided that has as an active ingredient thereof a human antibody light chain that demonstrates cytotoxicity against cancer cells and particularly lung cancer cells. The anticancer agent of the present invention primarily comprises: a human antibody κ-type light chain in the form of a dimer in which the variable region is composed of a polypeptide represented by the amino acid sequence of SEQ ID NO: 1, 9 or 13 or an amino acid sequence in which one or a plurality of amino acids have been added, deleted or substituted in these amino acid sequences; or, a human antibody κ-type light chain in the form of a monomer in which the variable region is composed of a polypeptide represented by the amino acid sequence of SEQ ID NO: 19 or an amino acid sequence in which one or a plurality of amino acids have been added, deleted or substituted in the amino acid sequence.