Provided are a novel pyridonecarboxylic acid derivative or a salt thereof having an excellent effect on bacteria such as methicillin-resistant Staphylococcus aureus, Pseudomonas aeruginosa, and Clostridium difficile and being not susceptible to drug efflux pumps and an antimicrobial agent comprising the same. A pyridonecarboxylic acid derivative represented by the Formula (1), wherein R 1 is a hydrogen atom, a halogen atom, a lower alkyl group or an amino group； R 2 is a group -NH-R 6 , wherein R 6 is a hydrogen atom, a lower alkyl group, an amino lower alkyl group, or the like； a group -O-R 7 , wherein R 7 is a hydrogen atom, a lower alkyl group, or the like； a group -(CH 2 ) m -R 8 , wherein R 8 is an amino group or the like and m is an integer of 1 to 4)； or a cyclic amino group represented by the following Formula (2), wherein Y represents NH or C-R 9a R 9b , wherein R 9a and R 9b are each independently a hydrogen atom, a lower alkyl group, an amino group, a lower alkyl amino group, or the like； and n and p are an integer of 1 or 2； R 3 is a hydrogen atom, a halogen atom, a lower alkyl group, or the like； R 4 is a hydrogen atom or a carboxyl group-protecting group； and R 5 is a hydrogen atom or a hydroxyl group-protecting group； or a salt thereof.
