The direct method developed in the first paper (J. Comp. Sci. Tech. 6 (2012), 147-156) to solve the finite-difference systems for Poisson's equation is extended to the cases with more complex boundary conditions. The first case is the plasma reactor of the international standard and the second is the three-dimensional plasma reactor. In the first case the computer execution time for the present method is 1 to 3% of the time for SOR with Chebyshev acceleration. In the second case the computer time for the present method is nearly the same as that for FFT method.