Novel cephalosporin derivatives, namely pivaloyloxymethyl 7.beta.-[2-(2-aminothiazol-4-yl)acetamido]-3-[[[1-(2-dimethylaminoethyl)-1H-tetrazol-5-yl]thio]methyl]-ceph-3-em-4-carboxylate and its pharmaceutically acceptable acid addition salts are found to be useful as orally administrable antibiotics having broad antimicrobial activities against both gram-positive and gram-negative bacteria.