An antibacterial agent is provided which is a cephem compound of the formula: ##STR1## wherein R.sup.1 is an acyl group; R.sup.2 is a carboxy group which may be esterified; R.sup.3 is a hydrogen atom, a lower alkyl group or cyano group; R.sup.4 is a hydrogen atom or a lower alkyl group, or R.sup.4 together with R.sup.3 is a methylene chain having 2 or 3 carbon atoms; R.sup.5 is a hydrogen atom or a lower alkyl group; A is an optionally substituted bivalent aromatic heterocyclic group which is bonded to a ring-constituting carbon atom with the adjacent sulfur atom; Y is a binding arm, sulfur or oxygen atom, --NH--, --CONH-- or --NHCO--; Z is a binding bond or --NH--; m is an integer of 0 to 4 and n is an integer of 0 to 6, or a pharmacologically acceptable salt thereof.