Antibacterial agents which are excellent in antibacterial activity and safety and comprise compounds represented by general formula (I), their salts, or hydrates of the same, wherein R1 represents hydrogen or alkyl; R2 represents hydrogen or alkyl; R3 and R5 represent each hydrogen; R4 represents hydroxy, halogeno, carbamoyl, alkyl, alkoxy or alkylthio; R6 and R7 represent each hydrogen or alkyl; n is an integer of from 1 to 3; R4 and the substituent on the pyrrolidine ring of general formula (III) are arranged at the cis-configuration; and Q is a partial structure represented by general formula (a).