1,2,4-Thiadiazole compounds represented by the formula (1) have excellent control activities against harmful arthropods: ##STR00001## wherein R.sup.1 represents C3-C7 alkynyl group optionally substituted one or more halogen atom(s); R.sup.2 a represents a halogen atom, a C1-C4 alkyl group, a C1-C4 haloalkyl group, a C1-C4 alkoxy group, a C1-C4 haloalkoxy group, a C1-C4 alkylthio group, a cyano group, or a nitro group, and n is an integer of 0 to 5, provided that, when n is an integer of 2 or more, respective R.sup.2s may be the same or different; A represents an oxygen atom, a sulfur atom, a single bond, a CR.sup.3R.sup.4 group, or NR.sup.5; R.sup.3 and R.sup.4 represent each independently a hydrogen atom or a C1-4 alkyl group; and R.sup.5 represent a hydrogen and the like.