Crack propagating evaluation is needed to predict and prevent structural damages since many structure defects from numerous crack propagating. It is widely known that ductile fracture occurs when external load is exerted to the material, these load include strong and unpredictable load such as earthquakes and collision of objects. Ductile material fractures via nucleation of void, growth of void and coalescence of voids. Many studies have been conducted; Kikuchi and Sannoumaru have published papers on the studies of ductile fracture. In the first paper , the thickness effect on the microscopic fracture process and fracture toughness is studied experimentally. In the second paper , dimple fracture tests were performed using three point bending specimens. In the test, loading condition is changed from mode I to mixed mode condition to study the effect of the mixed mode loading. Numerical simulation is conducted using Gurson’s constitutive equation. It is found that crack growth direction is affected significantly by the loading condition. Ductile fracture of a pipe used in Light Water Reactor components is researched in this paper. Four point bending of a pipe experiment had been done by the Central Research Institute of Electric Power Industry . They were experimented in two conditions; one at room temperature (23 ) and second at high temperature (300 ). As a result, crack propagation behavior differs largely form each other. At room temperature, crack propagates parallel from the pre crack, and at high temperature, crack propagates in a slanting direction from the pre crack. Results show that that difference from the two temperature distinction of a tensile test in a stress strain curve is very little. In this paper, this problem is studied at first by experiments, observation of fracture surface and numerical simulation.