Optically active pyrrolidine derivative represented by the following formula (XI): ##STR1## wherein R.sup.1 represents a benzyl group R.sup.2 represents an alkyl group having 1 to 6 carbon atoms, R.sup.3 represents an alkyl group having 1 to 6 carbon atoms, a benzyl group or an allyl group, R.sup.4 is selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 6 carbon atoms which may be substituted with a protected hydroxyl group, a vinyl group, a phenyl group which may be substituted, a benzyl group which may be substituted, and a heterocyclic ring having 1 to 4 nitrogen or/and oxygen atoms, and R.sup.5 represents a hydrogen atom or a methyl group. This compound can be an intermediate for synthesis of carbapenem antibiotic compounds.