This papers deals with overall phase transformation kinetics. The Fokker-Planck type equation is derived from the generalized nucleation theory proposed by Binder and Stauffer. Existence of the steady state solution is shown by a method based on the mean value theorem of differential calculus. From the analysis of asymptotic behavior of the Fokker-Planck type equation it is known that the number of clusters having the critical size increases with time in the case of constant driving force. On the basis of the present study on overall phase transformation kinetics a simple method for analyzing experimental phase transformation curves was proposed.