Disclosed are a novel medicinal agent, a novel health food and the like, each of which comprises a short peptide as an active ingredient, which is safe, inexpensive and effective, and which has a novel anti-tumor effect, wherein the short peptide is derived from a probiotic (an enterobacterium which lives symbiotically in a human intestine) and can be chemically synthesized readily. Specifically disclosed are an activator for an insulin-like growth factor-binding protein and an anti-tumor agent for gastrointestinal cancer including colorectal cancer, each of which comprises plantaricin-A (one of bacteriocins) secreted from Lactobacillus plantarum and composed of 26 amino acid residues or CSF (competence and sporulation factor) secreted from Bacillus subtilis and composed of 5 amino acid residues as an active ingredient.
