An optically active sulfoxide compound that is useful as an intermediate for synthesis or an active ingredient of a physiologically active substance such as a pharmaceutical agent is produced at a high optical purity. A process for producing an optically active sulfoxide compound of formula (4) comprises oxidizing a sulfide compound of formula (3) in the presence of an optically active metal complex of formula (1), (1′), (2) or (2′) by using an oxidizing agent. The present invention is also directed to the optically active metal complex.