  We investigate the properties of the nonequilibrium steady state for the
stochastic system driven by a nonlinear drift force and influenced by noises
which are not identically and independently distributed. The nonequilibrium
steady state (NESS) current results from a residual part of the drift force
which is not cancelled by the diffusive action of noises. From our previous
study for the linear drift force the NESS current was found to circulate on the
equiprobability surface with the maximum at a stable fixed point of the drift
force. For the nonlinear drift force, we use the perturbation theory with
respect to the cubic and quartic coefficients of the drift force. We find an
interesting potential landscape picture where the probability maximum shifts
from the fixed point of the drift force and, furthermore, the NESS current has
a nontrivial circulation which flows off the equiprobability surface and has
various centers not located at the probability maximum. The theoretical result
is well confirmed by the computer simulation.
