A method of operation for an injection molding machine is disclosed. The injection molding machine includes an injector having an advancable screw and a barrel cylinder, and a mold clamp for holding a mold with a controllable pressure and for allowing the mold to open a controllable amount. In performing the method, preset values are established for a stop position of the advancable screw, a clamping pressure of the mold clamp, and an opening amount for the mold. The screw is advanced up to the preset stop position and stopped thereat. The screw is controlled so as to ensure the location of the screw at the preset stop position for a preset time. Resin is injected from the barrel cylinder into the mold. The mold is clamped with the preset clamping pressure, during the preset time, by operating the mold clamp while maintaining the positioning of the screw at the preset stop position. Further, the mold clamp is operated to controllably allow for opening of the mold during the injecting step, so that the mold is allowed to open to the preset opening amount when the injecting step is completed.