  We present a lattice QCD study for the cutoff effects on nuclear forces.
Two-nucleon forces are determined from Nambu-Bethe-Salpeter (NBS) wave
functions using the HAL QCD method. Lattice QCD simulations are performed
employing N_f = 2 clover fermion configurations at three lattice spacings of a
= 0.108, 0.156, 0.215 fm on a fixed physical volume of L^3 x T = (2.5 fm)^3 x 5
fm with a large quark mass corresponding to m_\pi = 1.1 GeV. We observe that
while the discretization artifact appears at the short range part of
potentials, it is suppressed at the long distance region. The cutoff dependence
of the phase shifts and scattering length is also presented.
