A carbapenem derivative represented by the following formula (I), ##STR1## wherein R.sub.1 represents a hydrogen atom, a substituted or unsubstituted aryl group, or a substituted or unsubstituted heterocyclic group, R.sub.2 indicates a hydrogen atom or a protective group for a carboxyl group, and R.sub.3 is a methyl group or an ethyl group; or a pharmaceutically acceptable salt thereof, and a pharmaceutical composition comprising this carbapenem derivative or a salt thereof as an active ingredient. The carbapenem derivative exhibits a wide and strong antimicrobial activity, particularly a strong antimicrobial activity against MRSA. An intermediate compound for preparing the carbapenem derivative is also disclosed.