In the previous reports, the authors have clarified the brittle fracture characteristics of multiple notches arranged in a straight line, in parallel and in parallel staggered in the crosswise direction to load, by tests with mother plate specimens. On the other hand, however, because defects forming the notches often exist in weld joints in steel structures, residual stress or change in material quality due to the weld will give influence, which are not negligible, upon the brittle fracture characteristics of multiple notches. In this report, the above mentioned influences are examined with 4 kinds of example representing the defects existing in the weld joints and by conducting two kinds of test, viz. a Moiré test at room temperature and a brittle fracture test at low temperature for these examples. As a result, it has been made clear that the fracture occurs when a crack opening displacement (Φ) calculated by the following equation has exceeded a critical crack opening displacement (Φ _c ). Φ= f_R ·g (λ) ·Φ _s =Φ _c where : f_R : Coefficient of influence by residual stress. g (λ) : Coefficient of interaction effects of notches. Φ _s : Crack opening displacement at the time when a single notch exists in the mother plate. The influence of residual stress can be estimated by f_R and the influence by material deterioration can be estimated by the decrease of Φ _c .