A fused heterocyclic compound the formula (1): wherein A 1 represents -NR 8 -, and the like; A 2 represents a nitrogen atom, and the like; A 3 represents a nitrogen atom, and the like; R 1 represents an ethyl group; R 2 , R 3 , R 4 , and R 5 are same or different and represent independently a C1-C6 chain hydrocarbon group optionally having one or more halogen atoms, and the like; R 6 and R 7 are same or different and represent independently a C1-C6 chain hydrocarbon group optionally having one or more atoms or groups selected from Group X, and the like; R 8 represents a C1-C6 chain hydrocarbon group optionally having one or more atoms or groups selected from Group W, and the like; n represents 0, 1 or 2. The compound has an excellent activity of controlling pests.