Disclosed is a peptide consisting of an amino acid sequence represented by formula (I), and having highly-shifted accumulation to digestive system cancer cells and tissues: in the formula (I), X11is peptide residue consisting of the following amino acid sequence of (a) or (b)； (a) an amino acid sequence set forth in any one of SEQ ID NOS:1, 2, and 3； and (b) an amino acid sequence comprising a sequence in which one or two amino acids have been deleted, substituted or added in the amino acid sequence set forth in any one of SEQ ID NOS:1, 2, and 3； Y11is a peptide linker consisting of one or more and ten or less of the amino acid residues, each of which independently is glycine residue, proline residue, serine residue, cysteine residue or lysine residue ； X12is peptide residue consisting of the said amino acid sequence of (a) or (b), or retro-inverso peptide residue of them； n11 is an integer of one or more and nine or less.[Formura 1]X11-(Y11-X12)n11(I)係由通式(I)所示之胺基酸序列所構成，且對消化系統的癌細胞或是癌組織具有高度的累積性。(通式(I)中，X11係由以下的(a)或是(b)的胺基酸序列所構成之肽殘基；(a)序列編號1至3之任一者所示之胺基酸序列；(b)序列編號1至3之任一者所示之胺基酸序列中，含有1或是2個的胺基酸缺失、取代或是加成之序列之胺基酸序列；Y11係胺基酸數1以上10以下的胺基酸殘基所構成之肽連接體，前述胺基酸殘基係各自獨立，為甘胺酸殘基、脯胺酸殘基、絲胺酸殘基、半胱胺酸殘基或是離胺酸殘基；X12係由前述(a)或是前述(b)的胺基酸序列所構成之肽殘基、或是該等的逆反型肽殘基。n11為1以上9以下的整數。)X11－(Y11－X12)n11(I)
