Disclosed are: an agent for inhibiting the production of active oxygen from an intestinal epithelium cell； an agent for inhibiting the production of IL-8 from an intestinal epithelium cell； and a prophylactic and therapeutic agent for inflammatory bowel disease and/or irritable bowel syndrome, each of which comprises a fermentation product, a culture supernatant and/or a culture of a bacterium belonging to the genus Bacillus as an active ingredient. The bacterium belonging to the genus Bacillus is preferably Bacillus subtilis, more preferably Bacillus subtilis C-3102 (FERM BP-1096). The agent for inhibiting the production of active oxygen from an intestinal epithelium cell, the agent for inhibiting the production of IL-8 from an intestinal epithelium cell, and the prophylactic and therapeutic agent for inflammatory bowel disease and/or irritable bowel syndrome can be administered through an oral route and are useful for the treatment and prevention of diseases including ulcerative colitis, Crohn's disease and irritable bowel syndrome.
