A compound represented by the general formula (I) or a salt thereof which has excellent antibacterial activity (R.sub.1 represents hydrogen atom or an alkylcarbonyl group, R.sub.2 represents hydrogen atom, oxygen atom, hydroxyl group, or an alkylcarbonyloxy group, for example, when R.sub.2 is hydrogen atom, R.sub.3 represents group (a) (each of R.sub.5 and R.sub.6 represents hydrogen atom or an alkyl group), R.sub.4 represents hydrogen atom or group (c) (each of R.sub.8 and R.sub.9 represents hydrogen atom or an alkylcarbonyl group), and Me represents methyl group). 1