The present invention relates to a production method of an optically active form of a compound represented by formula (II) ##STR1##

wherein ring A is a benzene ring optionally having substituent(s); R¹ is H, a hydrocarbon group optionally having substituent(s), an acyl group or an acyloxy group; R², R³ and R⁴ are each H, an alkyl group optionally having substituent(s), an alkoxy group optionally having substituent(s) or an amino group optionally having substituent(s); X is N or CH; Y is N or CH; and * shows an asymmetric center, or a salt thereof, which includes reacting a compound represented by the formula (I) ##STR2##

wherein each symbol is as defined above, or a salt thereof, with an excess amount of an oxidizing agent in the presence of a catalyst for asymmetric induction, and provides an efficient production method of an optically active sulfoxide derivative in high yield on an industrial large scale by a convenient method, while achieving an extremely high enantiomer excess.