[Problem] The present invention pertains to a safer and more efficient therapeutic agent for respiratory tract infections. [Solution] A therapeutic agent for aspiration pneumonia, lung suppuration, or lung abscess, the agent containing as an active ingredient 7-[(3S,4S)-3-{(cyclopropylamino)methyl}-4-fluoropyrrolidin-1-yl]-6-fluoro-1-(2-fluoroethyl)-8-methoxy-4-oxo-1,4-dihydroquinoline-3-carboxylic acid or a pharmaceutically acceptable salt thereof.