<;P>;PROBLEM TO BE SOLVED: To provide an antimicrobial agent having a strong antimicrobial activity and high safety. <;P>;SOLUTION: A compound represented by general formula, e.g. 7-chloro-1-(2-(4-((2,3-dihydro(1,4)dioxino(2,3-c)pyridin-7-ylmethyl)amino)piperidin-1-yl)ethyl)-1,5-naphthyridin-2(1H)-one, 1-(2-(4-((2,3-dihydro(1,4)dioxino(2,3-c)pyridin-7-lymethyl)amino)piperidin-1-yl)ethyl)-7-fluoro-1,5-naphthyridin-2(1H)-one, or 1-(2-(4-((2,3-dihydro(1,4)dioxino(2,3-c)pyridin-7-ylmethyl)amino)piperidin-1-yl)ethyl)-7-methoxy-1,5-naphthyridin-2(1H)-one. <;P>;COPYRIGHT: (C)2009,JPO&INPIT