An enantiomer preparation method in which one enantiomer of a sulfoxide compound is selectively prepared, the sulfoxide compound having a sulfur atom of a sulfoxide group as an asymmetric center, the method including a step A for optically resolving an enantiomer mixture of a sulfoxide compound into one enantiomer and the other enantiomer; a step B for irradiating with light the other enantiomer obtained in step A or step C to racemize the enantiomer; and step C for optically resolving the enantiomer mixture of the sulfoxide compound obtained in step B into one enantiomer and the other enantiomer. A system for preparing an enantiomer which is used in the enantiomer preparation method.