A numerical simulation method for predicting transport and melting phenomena of Mg alloy particles in an injection molding machine was developed in the present study. Mg alloy particles in the screw groove were treated as a porous material in order to simplify governing equations. The apparent physical properties of the porous material were evaluated with the empirical formulations derived in our previous works. Some other model constants were determined by comparing the numerical and experimental results. As a result, the followings were obtained. The bulk density of the porous material was increased rapidly at a certain position in an injection molding machine. The increasing rate of the bulk density became remarkable in a case of shallower screw groove. The relative angular velocity of Mg alloy against the screw at the inlet was not affected by the angular velocity of the screw at a fixed groove depth, however it was increased with an increasing in the depth of the screw groove at a fixed angular velocity of the screw. At a constant mass flow rate of Mg alloy, the outlet temperature of Mg alloy was increased with an increase in the depth of the screw groove. However, the torque required for screw rotation was not affected by the depth of the screw groove.