Top Quark Mass determination at the ATLAS experiment using early data

The ATLAS experiment will start taking data at the end of 2007. During the very first data taking period it will be possible to make a preliminary measurement of the top quark mass in the semileptonic decay channel of ttbar events. A possible strategy to perform this measurement is presented with particular interest in the role of jet energy scale: a jet calibration algorithm is developed and results are discussed. A detailed discussion of test beam data is also presented together with comparisons of Monte Carlo predicions.