PROBLEM TO BE SOLVED: To provide a pharmaceutical agent which shows strong antibacterial activity against gram-negative bacteria such as Pseudomonas aeruginosa and a drug resistance bacterium thereof based on an LpxC inhibiting action, and contains a new compound as an active component.SOLUTION: The preventive or therapeutic agent for infectious diseases having a gram-negative bacterium as a causative bacterium contains a hydroxamic acid derivative represented by general formula or a pharmaceutically acceptable salt thereof as an active component.