The present invention provides a controlling agent for a disease caused by a Clostridium bacterium, comprising a cashew nut shell liquid, a heat-treated cashew nut shell liquid, anacardic acid, cardanol, or anacardic acid and cardanol.本發明係提供特徵為含有腰果殼油、經加熱處理之腰果殼油、檟如酸、腰果酚,或檟如酸與腰果酚之梭菌屬細菌所引起之疾病的防治劑。