Disclosed are a cephalosporin compound of the formula
wherein:
R¹ is an optionally protected amino group,
R² is a substituted or unsubstituted heterocyclic group having 1 to 3 hetero atoms selected from the group consisting of nitrogen and sulfur, and
R³ is an optionally protected carboxyl group or a group -COO⁻, or a salt thereof, processes for their preparation and the use thereof. The cephalosporin compound or a salt thereof is useful as an antimicrobial agent.