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, R1 is, for example, a C1˜C6 alkyl group which is mono- or poly-substituted with halogen atom; R2 is, for example, a halogen atom or a C1˜C6 alkyl group; R3 is, for example, a hydrogen atom or a halogen atom; and R4 is, for example, a hydrogen atom or a C1˜C12 alkyl group.] The derivative or the salt has an excellent pest control effect.