It becomes possible to reduce the amount of an intestinal putrefacted substance effectively by the efficient use of a highly safe and useful microorganism. Attention is focused on bifidobacteria which are believed to be predominant generally in a human living body (intestine) and the screening of bifidobacteria is carried out. As a result a bifidobacterium strain which has a potent indol amount reduction activity and of which the activity of reducing the amount of indoxyl sulfate in serum has been confirmed can be selected.
