Fracture phenomenon of rubber has not been elucidated yet because the fracture is localized in molecular level at the initiation and it rapidly grows to form the semi-macroscopic crack. To resolve the phenomena, we performed molecular simulations of rubber with a coarse-grained model of the polymer and the solid fillers. We used the K-computer to attain 137 million particles system that is comparable to the volume of 350x350x350 nm3 in a real rubber. We applied the step stretch to the system and observed the void nucleation and the successive pattern formation. We observed two different dynamical processes in the structure growth during the elongation: 1) the nucleation-growth of cavity in the polymer network and 2) a spinodal-like void growth in vicinity of the polymer–particle interface.