The author carried out experimental and analytical investigations for the purpose of finding out the method of judging the safety of ship hull structural members containing fatigue cracks by means of Fracture Mechanics. In the first place, fatigue crack propagation tests were carried out under constant stress condition on the corner models and slot part model of ship hull structures, and for specimens with a center notch, similar test were also conducted under two different stress conditions. From these test results, he cleared the applicability of fatigue crack propagation law, da / dN = C · ΔK ^m , to structure model, and the returdation of fatigue crack growth in the case of changing the stress from higher to lower. Next, using these experimental data and calculated results he investigated both the design curves for fatigue crack propagation and those for fracture in order to judge the safety or residual strength of structural members containing fatigue cracks.