In plastic injection molding, the tip of the nozzle is touched to the mold and molten resin is filled into the mold. While the tip of the nozzle is in contact with the mold during plasticization, the temperature at the tip of the nozzle is cooled by being taken by the mold, but retreating plasticization is the same as insulating the tip, so the nozzle tip temperature rises. By controlling the timing of advance and retreat of plasticization, it is also possible to control the nozzle tip temperature and take measures against defects. By lowering the tip temperature with the forward hold, stringing can be eliminated, and with the retraction after measurement, the tip temperature can be prevented from dropping and a cold countermeasure can be taken. Depending on the conditions of the plastic resin molding, it is necessary to selectively use plasticizing advance holding and retraction after measurement.