A free energy landscape (FEL) picture of the glass transition is presented, which provides a unified understanding of glass transition singularities.This view is a straight forward generalization of the Landau theory of phase transitions with atomic configuration in place of the order parameter.Exploiting the density functional theory, we show that the FEL can really be calculated and argue that there are two kinds of cooperatively rearranging regions: One is the region defined by the difference between two adjacent basins, which could be called a simultaneously rearranging region, and the other is the atoms involved in the excited state between two adjacent basins.We obtain the FEL for a relaxation process which is characterized by a string motion and determine the size of the cooperatively rearranging region.