An equation of the threshold stress intensity factor range was proposed for the fatigue crack growth using a nonlinear region of unique fatigue fracture. The following phenomena, peculiar to the peening specimen with a pre-crack, were analyzed using previous experiment results based on the proposed equation. As a result, the following ① to ④ phenomena could be evaluated quantitatively whereas ⑤ was evaluated qualitatively. ① Pre-crack size that can be rendered harmless by peening; ② Fatigue limit of pre-crack specimen that cannot be rendered harmless; ③ A phenomenon that fatigue fracture appears from outside the pre-cracked part on most of the harmless pre-crack specimen; ④ Non-propagating crack condition of stage II (tensile type), observed in most specimen showing fatigue limit; and ⑤ Qualitative analysis for initiation of non-propagating stage II crack (tensile type) in the peening specimen based on the reference regarding to a micro distribution of residual stress due to peening.