This invention provides a quinolone derivative which exerts strong antibacterial action upon various bacteria and has high safety, and it relates to a compound having a structure of formula (I), its salts and hydrates thereof: {R1 and R2: hydrogen, alkyl; n: 1 to 4; Q: following structure (Ia): [R3: alkyl, alkenyl, halogenoalkyl, cyclic alkyl, aryl, heteroaryl, alkoxyl, alkylamino; R4: hydrogen, alkylthio; R5: hydrogen, amino, hydroxyl, thiol, halogenomethyl, alkyl, alkenyl, alkynyl, alkoxyl; X1: halogen, hydrogen, A1: nitrogen, structure of formula (II): (X2: hydrogen, amino, halogen, cyano, halogenomethyl, halogenomethyl, alkyl, alkenyl, alkynyl, alkoxyl; R4 and R3 or X2 and R3 may together form a cyclic structure; Y: hydrogen, various ester forming groups]}.