Welded and notched wide plate specimens of high tensile structural steel were tested in constant load tests and constant net section stress tests, and welded and notched wide plate specimens and notched wide plate specimens of mild steel were also tested in constant load tests. In each test series three kinds of initial notch lengths were provided in order to determine the effect of material properties at notch root ; mother metal, heat affected zone and deposited metal. As a result of the tests it was found that the material properties at notch root and residual stress influence very little the initiation and propagation behavior of the low cycle fatigue crack, if weldment matches mother metal well, and that fatigue crack propagation rate changes in accordance with the change of the mode of fatigue crack.