The present invention provides a compound represented by the formula (I) wherein X is a hydrogen atom or a fluorine atom； R is a hydrogen atom or alkyl； R 1 is (1) cyclopropyl optionally substituted by 1 to 3 halogen atoms or (2) phenyl optionally substituted by 1 to 3 halogen atoms； R 2 is alkyl, alkoxy, haloalkoxy, a halogen atom, cyano, etc.； and R 3 is 7-oxo-7,8-dihydro-1,8-naphthyridinyl, 3-pyridyl, etc., or a salt thereof. The compound of the present invention has excellent antimicrobial activity against Clostridium difficile and is useful for the prevention or treatment of intestinal infection such as Clostridium difficile- associated diarrhea.
