The present invention has a broad antibacterial spectrum, to provide new compounds which exhibit potent antimicrobial activity against particular β- lactamase producing Gram negative bacteria. Specifically, the present invention provides a compound of formula (I)

(Wherein, the meanings of the symbols are as defined in the specification) a compound represented by, or protected form or their in the amino group when present is an amino group on the ring in the 7-position side chain providing pharmaceutically acceptable salts and pharmaceutical compositions containing them.