PURPOSE: To obtain a mono- or polyalkoxylated aromatic compd. in a high yield from an arom. compd. having at least one piece of halogen atom by using a solvent which is not so much costly and may be easily recirculated.

CONSTITUTION: The compd. of formula I ((m) is an integer of ≥1; (n) is an integer of ≥0; more preferably m+n is 1 to 6; X is I, Br, Cl; R0 is a (substd.) arom. cyclic group having at least 5 atoms within the ring) and the compd. of formula II (M is an alkal metal, alkaline earth metal: (w) is valance of M; R is a 1 to 12C hydrocarbon group) are reacted in the presence of a copper catalyst, to produce the compd. of formula III (R1 is a 1 to 6C linear or branched chain alkyl). At this time, an effective amt. of a promoter selected from among formamides and their acetals is made to exist in the reaction system described above, by which the compd. described above is advantageously obtd. without the need for protecting an aldehyde functional group even if the raw materials contain the group. The alkylation reaction may be continuously executed in the same reactor after the end of the reaction described above.