The method of Calculating effectiveness factor of the porous catalyst, which factor depends upon the diffusibility of reactants or products insid catalyst as well as on the pure chemical reaction, had formerly been developed to the first order reaction or to a few other cases. Whereupon the authors have tried and succeeded in extending its application to the cases in general in which chemical reaction rates are given and equations are presented as a function of constitution. As an example, the calculation method for ammonia synthesis is illustrated.