A quinolone synthetic antibacterial agent having excellent properties as amedicine is provided, which has strong antibacterial activity not only to Gram-negativebacteria but also to Gram-positive cocci that have low sensitivity to quinoloneantibacterial agents, and which exhibits high safety and excellent pharmacokinetics.A compound represented by the formula (I) or a salt thereof, or a hydrate thereof.Specifically, a quinolone derivative of the formula (I) wherein substituentsR6 and R7 taken together with the carbon atoms to which they are bonded form a cyclicstructure which may contain an oxygen atom as a ring constituent atom, the cyclicstructure forming a 5-4, 5-5, or 5-6 fused bicyclic pyrrolidinyl substituent,the substituent being bonded to a quinolone mother skeleton Q containing a pyridobenzoxazinestructure.
