Powder Injection Molding (PIM) is an important manufacturing technology for the net-shape production of precise metal or ceramic components. To improve productivity for multi-cavity molds, it is a key factor to shorten cycle time required. One of barriers to successfully manufacture injection molded articles using a multi-cavity mold is filling imbalance, possibly leading to defect in sintering stage. There are many factors with an influence on filling imbalance. Among such factors, we investigate the effect of the thermal conductivity of the PIM feedstock, which has a significant effect on the temperature distribution within a delivery system of the mold. Even in a geometrically symmetric delivery system, it is known that asymmetric branching of flow paths occurs due to the flow resistance affected by the temperature-dependent viscosity of the feedstock. The asymmetric filling may limit the benefit of using a multi-cavity mold. In this study, we developed a three-dimensional filling simulation code for PIM and applied the developed code to investigate the filing imbalance in the delivery system of a multi-cavity mold. A stabilized finite element method is employed to solve the flow and the heat transfer problems in filling stage. As for the melt front capturing, a level set method is used. From simulations, it is found that filling imbalance is caused by the non-uniform molding cooling, the thermal conductivity of the feedstock, and the viscous heating near the skin layer. We also compared filling pattern showing filling imbalance obtained from numerical simulations with those observed experimentally.