Provided is a novel anticariogenic agent having no side effects, said anticariogenic agent being capable of exerting an anticariogenic effect even on people who are highly sensitive to oligosaccharides or sugar alcohols. Also provided is an agent for preventing periodontal diseases or an agent for treating periodontal diseases that is capable of exerting an effect of preventing or treating periodontal diseases and has little side effects. The present invention relates to an anticariogenic agent and an anticariogenic composition each containing a bifidobacterium, a bifidobacterium-containing agent and composition for preventing periodontal diseases, and a bifidobacterium-containing agent and composition for treating periodontal diseases.
