An industrially preferred process for producing an isothiazole compound, particularly 3,4-dichloro-5-cyanoisothiazole, provides a safer industrial production process by avoiding the simultaneous use of an aprotic polar solvent such as N,N-dimethylformamide and chlorine. In addition, a production process which is economically preferred because an aprotic polar solvent, which is highly likely to become a part of waste, is not used.A process for producing an isothiazole compound represented by a general formula (3), wherein R is a cyano group or the like; and X is a chlorine atom or the like, which comprises heating a nitrile compound represented by a general formula (1), wherein R is as defined above, and sulfur, and then carrying out a reaction between the nitrile compound represented by the general formula (1), the sulfur and a halogen represented by a general formula (2), wherein X is as defined above.