The main purpose of the present study was to prove the possibility of the intiation of brittle fracture originated under a low applied stress level and from a notch existing a severely stress concentrated region in a steel plate structure, in which any local welding stress is eliminated. And this purpose was accomplished for the first time by the successful results of the present study. Analyses of the results obtained led to the following major conclusions: When a sharp notch perpendicular to the loading direction exists in the discontinuous portion of a structure where a stress concentration is developed in loading condition due to structural discontinuities, such stress concentration may contribute as the predominant factor if only the ratio of stress concentration is high enough even though the residual welding stress in this part has been fully relieved. For instance, in the case of doubler plates as wide as the notch closing to each other with 30mm space over the notch, a brittle fracture initiated at a low temperature under a mean stress equal to 36% of the yield point of base metal at room temperature, in spite of the residual stress having been fully elimineted.