The present invention provides an antibacterial drug for intestinal bacteria such as Clostridium difficile which causes infectious diseases in humans.The present invention is an antibacterial agent for intestinal bacteria containing equol as an active ingredient.本發明提供一種對人類引起感染病之困難梭狀桿菌等腸內細菌之抗菌藥。本發明係一種包含雌馬酚作為有效成分之針對腸內細菌之抗菌劑。