The present invention provides a novel compound which has a wide antimicrobial spectrum, and in particular exhibits potent antimicrobial activity against beta-lactamase producing Gram negative bacteria. Specifically, the present invention provides a compound of the formula (I):wherein each symbol is as defined in the specification,or an amino-protected compound when the amino group is present on the ring in the 7-side chain, or a pharmaceutically acceptable salt thereof, and a pharmaceutical composition comprising the same.
