PROBLEM TO BE SOLVED : To provide a novel nuclear factorKB(NF kB) inhibitor. SOLUTION : A plant body of Plumbago zeylanica is subjected to extraction, a component contained in it is subjected to isolation and purification, and a naphthoquinone derivative represented by general formula (1) is isolated. The component has excellent KFKB inhibitory action. In general formula (1), one or both of R1, R2 is a group selected from a 2-methyl-5-hydroxy-1, 4-naphthoquinone residue, and an alkyl group and an alkenyl group optionally having a carbonyl group. A bond position of R1 and R2 may be anywhere in a ring, and a group of a dashed line may be present or not). SELECTED DRAWING : None COPYRIGHT : (C)2019, JPO&INPIT