Provided are a new peptide, a vector inserting a DNA that codes said peptide, a transformant obtained by transformation with that vector, and applications of said peptide, vector and transformant. The peptide comprises an amino acid sequence set forth in SEQ ID NO: 1, or an amino acid sequence obtained by substituting, deleting or adding one or more amino acids to/from the amino acid sequence set forth in SEQ ID NO: 1. This peptide and the vector inserting a DNA that codes this peptide are suitable for use in an agent for promoting the proliferation of pancreatic hormone-producing cells, or a differentiation induction promoter that induces differentiation to pancreatic hormone-producing cells.