Provision of new butyric acid-producing bacteria. A butyric acid-producing bacterium belonging to Clostridium leptum subgroup, which produces butyric acid and does not produce formic acid in a medium without acetic acid.新たな酪酸産生菌の提供。 酢酸非存在の培地において、酪酸を産生し、かつギ酸を産生しない、Clostridium leptum subgroupに属する酪酸産生菌。