A process for producing a sulfonyl chloride compound comprising:(A) a step comprising reacting a pyridazine compound represented by the formula (1): wherein R1 represents a hydrogen atom, a halogen atom, an alkyl group which may be substituted with a halogen atom or atoms, or the like, R2 and R3 are the same or different and each represents a hydrogen atom or the like, R4 represent a hydrogen atom, a halogen atom, an alkyl group which may be substituted with a halogen atom or atoms, or the like, with a sulfonating agent; (B) a step comprising contacting the reaction mixture obtained in the step (A) with a chlorinating agent; and (C) a step comprising mixing the reaction mixture obtained in the step (B) with an aqueous inorganic base solution to separate an organic layer containing a sulfonyl chloride compound represented by the formula (2): wherein R1 to R4 are the same meanings as defined above.