In recent years, high polymer products need superior mechanical properties in a particularly strength and dimensional accuracy of the products. One of the most famous molding method of polymer materials is an injection molding. The method is better at making a complicated shape at a short tact time, while it is fact that this has many kinds of molding faults. Various solutions to reduce these on a production line have been developed thanks to long years studies. However, it needs focusing on the basic state of plasticized resin. In the injection molding, it is important to find how uniform the resin is melted because the uniformity of temperature is related to product’s characteristics. Therefore, melting completion doesn’t mean the uniformity. The judge of uniformly melting must be cleared to achieve high quality. First of all, this study uncovers some effects of a screw behavior in the plasticization. Injection molding machine performs the metering and the injection processes by the screw in a barrel. In the metering process, it retreats to metering stroke keeping back pressure. In the injection process, it advances to a tip of a nozzle. The screw repeats these movements, so the pellets are provided from the hopper to the moving screw. This causes the difference of the distance for the resin to pass through the screw channel. The longest difference in an injection cycle is the same as the metering stroke. The resin’s viscosity clearly depends on the barrel temperature although it is also influenced by other molding conditions. Then, this experiment is made by changing the metering stroke and the barrel temperature. To understand the resin just before the injection, an original nozzle which can include a pressure sensor is produced. Thus, a waveform of the injection pressure can be taken every cycle. As the changes are reflected in the resin’s behavior, non-uniform temperature can be visually confirmed on the disturbance of the waveform.