A quinolone synthetic antibacterial agent and a therapeutic agent for an infection which exhibit broad spectrum and strong antibacterial activity for both Gram positive and Gram negative bacteria, and which are also highly safe are provided. The compound provided is represented by following formula (I): wherein R 1 and R 2 represent hydrogen atom, or the like； R 3 represents an alkyl group containing 1 to 6 carbon atoms, or the like； R 4 and R 5 independently represents hydrogen atom, an alkyl group containing 1 to 6 carbon atoms, or the like, with the proviso that R 4 and R 5 do not simultaneously represent hydrogen atom； or the substituents R 4 and R 5 together represent (a) a 3- to 6-membered cyclic structure including the carbon atom shared by R 4 and R 5 to form a spirocyclic structure with the pyrrolidine ring； R 6 and R 7 independently represents hydrogen atom, an alkyl group containing 1 to 6 carbon atoms, or the like； R 8 represents a halogen-substituted alkyl group containing 1 to 6 carbon atoms, or the like； X 1 represents hydrogen atom or a halogen atom； A represents nitrogen atom or a moiety represented by formula (II):
