The present invention relates to an optically active phthalamide derivative represented by the following formula (I): (wherein each of R1 and R2 represents H, optionally substituted C1-C6 alkyl, or C1-C6 alkoxycarbonyl; R3 represents C1-C6 alkyl; A represents H, C1-C6 alkyl, C3-C6 alkenyl, C3-C6 alkynyl, optionally substituted phenoxy C1-C6 alkyl, or the like; p represents 0, 1, 2, 3, or 4; q represents 0, 1, or 2; X represents halogen, CN, NH2, C1-C6 alkyl, C2-C6 alkenyl, C1-C6 alkylthio, or the like; m represents 0, 1, 2, 3, or 4; Y represents halogen, CN, NH2, C1-C6 alkyl, optionally substituted phenyl, or the like; n represents 1, 2, 3, 4, or 5; and each of Z1 and Z2 represents C—Y or N; and further X and Y may form a condensed ring together with carbon atoms adjacent thereto on a phenyl ring), a salt thereof, an agrohorticultural insecticide comprising the above derivative as an active ingredient, and a method of use thereof. The optically active phthalamide derivative of the present invention has superior control activity as an agrohorticultural insecticide, and has excellent effects even when the insecticide is used in admixture with other insecticides.