  We report on a \textit{NuSTAR} and \textit{Swift}/XRT observation of the
newly discovered X-ray transient MAXI J1820+070. \textit{Swift}/XRT and
\textit{NuSTAR} have concurrently observed the newly detected source on 14
March 2018. We have simultaneously fitted the broad-band spectra obtained from
\textit{Swift}/XRT and \textit{NuSTAR}. The observed joint spectra in the
energy range 0.6--78.0 keV are well modeled with a weak disk black-body
emission, dominant thermal Comptonization and relativistic reflection fraction.
We have detected a fluorescent Iron-K$\alpha$ line relativistically broadened,
and a Compton hump at $\sim$ 30 keV. We constrain the inner disk radius as well
as the disk inclination angle and their values are found to be
4.1$^{+0.8}_{-0.6}$ R$_{ISCO}$ (where R$_{ISCO}\equiv$ radius of the innermost
stable circular orbit) or 5.1$^{+1.0}_{-0.7}$ r$_{g}$ (where r$_{g}\equiv$
gravitational radius) and 29.8$^{+3.0}_{-2.7}$ $^\circ$ respectively. The best
fit broad-band spectra suggest that the source was in the hard state and
evolving. The source emission is best described by weak thermal emission along
with strong thermal Comptonization from a relatively cold, optically thick,
geometrically thin and ionized accretion disk. X-ray spectral modeling helps us
to understand the accretion and ejection properties in the vicinity of the
compact object.
