The time evolution of a plane pattern in Benard convection field is numerically simulated with the generalized Ginzburg-Landau evolution equation described with the pattern variable, and the obtained numerical results are compared with and discussed previous experimental and theoreticalesults. In spite of a single non-linear differential equation, the evolution equation derived phenomenally is able to express the various convection patterns: roll cells, hexagonal cells, zigzag-rolls, cross-rolls, and the wave number change observed in super-critical Rayleigh number. This approach makes the procedure for analysis of the phenomena accompanied with pattern formation extremely simplify.