In the first report, we proposed a fatigue crack propagation parameter Δ K_RP from the view point of the appearance of cyclic tensile plastic zone at a crack tip in replace of Δ K_eff based upon the crack opening load. Moreover the automatic measuring system was developed for the purpose of obtaining the re-tensile plastic zone's generated load (RPG load) as well as crack opening load and crack closing load during fatigue crack propagation. In this report, fatigue crack propagation tests of CT specimens were carried out with various stress ratios of constant amplitude loadings. Moreover Δ K_th tests with the conditions of constant stress ratio and constant maximum load with increasing stepwise minimum load were also carried out. These tests were conducted by using above developed system. It becomes clear that Δ K_RP gives the quantitative effect of stress ratio on fatigue crack growth rate and the relation of logarismic Δ K_RP and logarismic crack propagation rate appears to be linear in the wide range from very slow crack growth rate region to stable crack growth region. On the other hand, threshold phenomenon appears only circumstantially due to the paticular loading pattern on Δ K_eff based on the crack opening load and Δ K_eff^cl based on the crack closing load.