The problem addressed by the present invention is to provide compounds and pharmaceutical compositions that demonstrate strong antibacterial activity against gram-negative bacteria and drug-resistant gram-negative bacteria. Compounds represented by general formula [1] (in the formula, each symbol is as described in the specification.) or salts thereof have strong antibacterial activity against gram-negative bacteria, including Pseudomonas aeruginosa, and drug-resistant gram-negative bacteria, including multidrug-resistant Pseudomonas aeruginosa, and pharmaceutical compositions containing these compounds or salts are useful as antimicrobials.