  Recently a new approach to calculate the nuclear potential from lattice QCD
has been proposed. In the approach the nuclear potential is constructed from
Bethe-Salpeter (BS) wave functons through the Schroedinger equation. The
procedure leads to non-local but energy independent potential, which can be
expanded in terms of local functions. In several recent applications of this
method, local potentials, which correspond to the leading order (LO) terms of
the expansion, are calculated from the BS wave function at E~0 MeV, where E is
the center of mass energy. It is therefore important to check the validity of
the LO approximation obtained at E~0. In this report, in order to check how
well the LO approximation for the NN potentials works, we compare the LO
potentials determined from the BS wave function at E~45 MeV with those at E~0
MeV in quenched QCD. We find that the difference of the LO potentials between
two energies are not found wihin the statistical errors. This shows that the LO
approximation for the potential is valid at low energies to describe the NN
interactions.
