A butyrate-producing bacterium belonging to Anaerostipes hadrus is provided. The amount of butyrate produced is at least 1.5 times that of Anaerostipes hadrus YIT 10092T (DSM 3319T) and is measured by thawing a frozen stock solution of the bacterial strain (a 10% (w/v) skim milk-2% sodium glutamate solution with suspended bacterial cells) (cell count: 2.0 to 5.5×1010 cells/mL), inoculating the solution at 1% to 4 mL of a PY liquid medium supplemented with 33 mM sodium acetate and 0.5 (w/v) % glucose (PYGA medium), followed by anaerobic culture at 37° C. for 24 hours, then inoculating the culture solution at 1% to a PYGA medium, followed by anaerobic culture at 37° C. for 24 hours, then inoculating the culture solution at 1% to a PY medium containing 33 mM sodium acetate and 0.5 (w/v) % L-sorbose, followed by anaerobic culture at 37° C. for 24 hours, and then measuring the butyrate concentration.