A fused heterocyclic compound represented by formula (1) or an N-oxide thereof has an excellent control effect on pests: wherein A1 represents N or the like, A2 represents NR6 or the like, A3 represents CR12 or the like, R1 represents a C1 to C6 chain hydrocarbon group or the like, R2, R4 and R5 are the same or different and represent a C1 to C3 alkyl group optionally having one or more halogen atoms or the like, R3 represents a C1 to C6 chain hydrocarbon group or the like, R6 represents a C1 to C6 chain hydrocarbon group or the like, any one set of R9 and R10, R10 and R11, and R11 and R12 in R9, R10, R11 and R12, together with the carbon atoms to which they are bound, forms a ring, and n represents 0, 1 or 2.