Collapse of ring-stiffened thin cylindrical shell under external pressure can be divided into two kinds, one “Shell Collapse”, the other “Bodily Collapse”. The “Bodily Collapse” was named and proposed by Tokugawa as the originator in this study of the world, but subsequently it is called “General Collapse” in the United States. As for “Shell Collapse”, researches were made by both Tokugawa and Windenburg, and are sufficiently practical in respect of Mild Steel. But, since High Tension Steel with superior weldability came out in public sales, we carried out experiments to obtain its characteristic qualities. Regarding “Bodily Collapse” there are two Theories in Elasticity, one by Tokugawa, the other by Kendrick, but they have not been put into actual use yet. Formulae, either by Levy or by Lame, which are now adopted in actual designs, show considerable discrepancies, as far as their definite length are concerned, when compared with the experimental results. Therefore, we aimed at putting Tokugawa's Theory of Elasticity into actual design, this time. Now, let us take : ψ= P_K · D /2 S (1+σ _YF /σ _YS · F / l ' S ) ·σ _YS , B =σ _YS · (1+σ _YE /σ _YS · F / l ' S ) / E · ( D / L ) ( S / D ) ^1.5· ( I / l ' S ³/12) ^3/4 considering, ψ is “Mean Pressure Factor” and B is “Bodily Factor”. The relation of ψ and B is shown in Fig 9. When calculating moment of inertia of stiffener, the effective breadth can be adopted with three (3) S in case of inner stiffener, and one (1) S in case of outer stiffener. If ±10% of tolerance is permitted, Fig 9 may be used in the actual design as they are, regardless whether they are Mild Steel or High Tension Steel.