[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.
