Substituted cyclobutylamine derivativesb with a novel structure represented by the following formula (I), wherein R1 to R4 and Q each represents a specific substituent and, in particular, Q represents a quinolone derivative having a specific structure. These derivatives are useful as antibacterial compounds which have excellent antibacterial activity against a wide scope of bacteria including Gram-negative and Gram-positive bacteria, exert potent antibacterial activity particularly against methicillin-resistant Staphylococcus aureus (MRSA) strains, penicillin-resistant pneumococcus strains and quinolone-resistant bacteria, and are also possessed of both excellent pharmacokinetics and high safety.