2-Ethenylthio-type carbapenem derivatives of formula (I) or pharmaceutically acceptable salts thereof are provided. The compounds according to the present invention have potent antimicrobial activity and a wide antimicrobial spectrum against pneumococci including penicillin resistant Streptococcus pneumoniae (PRSP), Haemophilus influenzae including ²-lactamase-negative, ampicillin-resistant Haemophilus influenzae (BLNAR), and Moraxella (Branhamella) catarrhalis.