The threshold power for the transition from the L-mode to the H-mode is evaluated theoretically. The model of the L- to H-mode transition based on the bifurcation of the radial electric field at the edge is employed. Using the particle confinement time of the L-mode and the result of the analysis on the plasmas in the scrape-off layer (SOL), the parameter dependence of the threshold power for the L- to H-mode transition is obtained.