The excessive cooling in the filling stage of injection molding stops flow of polymer melt and gives insufficient filling of material in to the mold. In order to enhance the fluidity of the material，it is desirable to prevent the decrease in the temperature of molten polymer. One solution is radiative heating of molten polymer by lasers passing through the mold wall. The authors adopted ad iode laser，which allows comprehensively inexpensive equipments of light source. In this study，an experimental test of molding of disk with laser irradiation was performed and a numerical simulation for analyzing the temperature profiles within the flow of polymer melt was also investigated. The results show that the fluidity of polymer melt by laser heating is improved and it is especially effective at high injection rate.