To provide a pharmaceutical given by searching a component having action of inducing expression or accelerating production of antibacterial peptide defensin, containing the component as an active ingredient, and therefore having the action of inducing the expression or accelerating the production of the antibacterial peptide defensin, and to provide food and drink having the action.

The agent for inducing the expression or accelerating the production of the antibacterial peptide in a digestive tract tissue contains a mannan-containing component derived from yeast as the active ingredient. The mannan-containing component preferably has a mannose content of ≥60 mass%. The agent is used for inducing the expression or accelerating the production of α-defensin or β-defensin as the antibacterial peptide. The pharmaceutical and the food and drink contain the agent, respectively.