An alkyl phenyl sulfide derivative represented by the general formula [I] or an agriculturally acceptable salt thereof, and a pest control agent containing the derivative or the salt as an active ingredient. [in the above formula, R 1 is, for example, a C 1 ˆ¼C 6 alkyl group which is mono- or poly-substituted with halogen atom; R 2 is, for example, a halogen atom or a C 1 ˆ¼C 6 alkyl group; R 3 is, for example, a hydrogen atom or a halogen atom; and R 4 is, for example, a hydrogen atom or a C 1 ˆ¼C 12 alkyl group.] The derivative or the salt has an excellent pest control effect.本發明提供一種具有優異有害生物防治效果的烷基苯基硫醚衍生物或其鹽、含有其以作為有效成分之有害生物防治劑及其製造中間體。本發明的烷基苯基硫醚衍生物或其農業上容許的鹽係如通式[I]所示:[式中,R1係表示C1~C6鹵烷基等;R2係表示鹵原子、C1~C6烷基等;R3係表示氫原子、鹵原子等;R4係表示C1~C12烷基等]。本發明的有害生物防治劑及其製造中間體係含有該烷基苯基硫醚衍生物或其農業上容許的鹽作為有效成分。