The present invention relates to a polypeptide having an activity of suppressing aging; DNA encoding the polypeptide; a method for improving livestock, using the DNA; a recombinant DNA prepared by inserting the DNA into a vector; a transformant harboring the recombinant; a method for preparing the polypeptide of the present invention, using the transformant; an antibody which recognizes the polypeptide; a ligand for the polypeptide of the present invention; a compound inhibiting specific binding between the polypeptide and ligand of the present invention; a compound enhancing the expression of an aging-suppressing gene encoding the aging-suppressing polypeptide of the present invention; an oligonucleotide comprising a sequence of 10 to 50 nucleotides in the nucleotide sequence of the DNA; and a therapeutic agent for a syndrome resembling premature aging, a therapeutic agent for adult diseases or an aging-suppressing agent, using the same.