3-(1-Aminocycloalkyl)pyrrolidinyl-substituted-6-dehalodeno(hydrogen-substituted)quinolon carboxylic acid derivatives having specific substituents as represented by the following formula (I), its salts, and hydrates thereof exhibit a broad and potent antibacterial activity on gram-negative and gram-positive bacteria, in particular, resistant bacteria typified by gram-positive cocci, including MRSA, PRSP and VRE. Thus these compounds are usable as drugs.