  Transport equation of the galactic cosmic ray (GCR) is numerically solved for
qA>0 and qA<0 based on the stochastic differential equation (SDE) method. We
have developed a fully time-dependent and three-dimensional code adapted for
the wavy heliospheric current sheet (HCS). Results anticipated by the drift
pattern are obtained for sample trajectories and distributions of arrival
points at the heliospheric boundary for GCR protons. Our simulation reproduced
a 22-year cycle of solar modulation which is qualitatively consistent with
observations. Energy spectra of protons at 1 AU are calculated and compared
with the observation by BESS.
