<;P>;PROBLEM TO BE SOLVED: To provide an interleukin-12 (IL-12) production promoter useful for preventing and treating diseases such as infectious disease, tumor, allergy etc., caused by IL-12 production deficiency. <;P>;SOLUTION: The interleukin-12 (IL-12) production promoter is obtained by combining a bacterium having an IL-12 production inducing ability with a treated virus or bacterium having a flagellum. The bacterium having an IL-12 production inducing ability is preferably Lactobacillus casei or Lactobacillus rhamnosus. The virus or bacterium having a flagellum is preferably rotavirus, Bacillus subtilis, Escherichia coli or salmonella. <;P>;COPYRIGHT: (C)2009,JPO&INPIT