Cancer antigen peptides derived from WT1 which have an in vivo efficacy, particularly a clinical usefulness, and cancer vaccines as dosage forms suitable for said cancer antigen peptides, are provided.The invention relates to water-in-oil emulsions which comprise as an effective ingredient either one or both of peptides selected from the group consisting of a peptide having an amino acid sequence of Cys Met Thr Trp Asn Gln Met Asn Leu (SEQ ID NO: 2), and a peptide having an amino acid sequence of Cys Tyr Thr Trp Asn Gln Met Asn Leu (SEQ ID NO: 3), as well as processes for preparation of said emulsion.