Inherent damage zone model assumes that the stress at a point which is located at a small distance, γ₀ from the crack initiation position governs the fatigue characteristics regardless of the geometric configuration of the specimen. The distance γ₀ represents the size of effective damage zone and it is an inherent length of the material. Ishibashi proposed the model to explain the difference between fatigue notch factor and stress concentration factor of notched specimen. This paper shows that the inherent damage zone model can explain several fatigue phenomena near the fatigue limit and the crack growth threshold consistently without restriction of smooth specimen, notched specimen or cracked specimens with short and long crack length. A special feature of the paper is using the exact solution of stress distributions of notched and cracked specimens. Neuber's analytical solution for notched specimen and Westergaard's stress function for cracked specimen are employed for this purpose. Relationship between fatigue limit of smooth specimen and threshold stress of cracked specimen, relationship of fatigue strength between round-shaped flaws and crack, occurrence condition of non-propagating crack at the root of sharp notch, and fatigue notch factor are discussed quantitatively based on the proposed model.