  In Monte Carlo simulation, lattice field theory with a $\theta$ term suffers
from the sign problem.
  This problem can be circumvented by Fourier-transforming the topological
charge distribution $P(Q)$. Although this strategy works well for small lattice
volume, effect of errors of
  $P(Q)$ becomes serious with increasing volume and prevents one from studying
the phase structure. This is called flattening. As an alternative approach, we
apply the maximum entropy method (MEM) to the Gaussian $P(Q)$. It is found that
the flattening could be much improved by use of the MEM.
