It is intended to provide a salt of a compound and crystals thereof useful as a therapeutic and/or preventive agent for infectious diseases which has wide and excellent antibacterial activity and has excellent safety. [Solution] The present invention provides the hydrochloride of 7-[(1R,5S)-1-amino-5-fluoro-3-azabicyclo[3.3.0]octan-3-yl]-6-fluoro-1-[(1R,2S)-2-fluorocyclopropan-1-yl]-1,4-dihydro-8-methyl-4-oxoquinoline-3-carboxylic acid and crystals thereof, as a novel salt form of the compound and crystals thereof.
