[Task] The present invention is to provide a 1,2-benzoisothiazole derivative or a salt thereof which is not harmful to a crop and is remarkably effective on an agricultural or horticultural plant disease such as Pyricularia oryzae, Septoria nodorum, Pseudoperonospora cubensis and Colletotrichum orbiculare, and, an agricultural or horticultural plant disease-controlling agent containing the derivative or its salt as an active ingredient. [Means] A 1,2-benzoisothiazole derivative represented by the general formula [I] (wherein R 1 is a hydrogen atom or a halogen atom, and R 2 is a methyl group or a halogen atom), or a salt thereof.本發明提供一種於作物不產生藥害，對於稻瘟病(rice blast)、小麥穎枯病(wheat glume blotch)、瓜類霜黴病(downy mildew)、瓜類炭疽病(clooetotrichum orbiculare)等農園藝用植物病害顯示顯著效果之1,2－苯并異噻唑衍生物或其鹽，及含有該衍生物或其鹽作為有效成分之農園藝用植物病害防除劑。；1,2－苯并異噻唑衍生物或其鹽係如通式[I]所示者：式中，R1表示氫原子或鹵素原子，R2表示甲基或鹵素原子。
