Abstract: The purpose of the present invention is to provide: a detection agent for specifically detecting cancer stem cells; a tumor antigen peptide specifically exhibited by cancer stem cells; a pharmaceutical composition for the prevention and/or treatment of cancer, containing same as an effective component thereof; and a method for screening said tumor antigen peptide. A peptide indicated by YO—XO—ZO, a polyepitope peptide including at least one said peptide as an epitope peptide and having a plurality of epitope peptides joined therein, a polynucleotide that codes at least either the peptide or the polyepitope peptide, a pharmaceutical composition containing these as an effective component thereof, and a cancer prevention and/or treatment agent characterized by inducing CTLs.