  The top quark mass plays an important role in a variety of discussions both
within and beyond the Standard Model. However, a precise determination of a
theoretically well-defined top quark mass is still missing. Towards a precise
determination of a theoretically well-defined top quark mass at the LHC, we
propose a method which uses lepton energy distribution and has a
boost-invariant nature. We investigate its experimental viability by performing
a simulation analysis for ttbar production process and lepton+jets decay
channel at the leading order. We estimate several major uncertainties in the
top mass determination with this method and they amount to 1.7 GeV with an
integrated luminosity of 100 fb^{-1} at sqrt{s}=14 TeV. The uncertainties
should be reduced by considering the next-to-leading order corrections to the
method.
