PROBLEM TO BE SOLVED: To provide an autoinducer-2 inhibitor which has activity of inhibiting autoinducer-2 and is effective for prevention, treatment and the like of infectious diseases.SOLUTION: An autoinducer-2 inhibitor includes at least one compound selected from a benzaldehyde derivative, a benzoic acid derivative and an acetophenone analog represented by specified formulae including general formula (1), as an active ingredient. In general formula (1), R, Rand Reach independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.【課題】オートインデューサー－２を阻害する活性を有し、感染症の予防及び治療等に有効な、オートインデューサー－２阻害剤の提供。【解決手段】一般式（１）を含む特定式で表わされるベンズアルデヒド誘導体、安息香酸誘導体、及びアセトフェノン類縁体より選ばれる少なくとも１種の化合物を有効成分とする、オートインデューサー－２阻害剤。（一般式（１）において、Ｒ１１、Ｒ１２及びＲ１３はそれぞれ独立に水素原子又は炭素数１以上６以下のアルキル基を表す。）【選択図】なし
