PURPOSE: To embody an optimum injection stage and stably obtain a required conforming article by a method wherein a resin sensor is provided in the path of a resin flow in a mold, and an objective speed change-over position is corrected on the basis of a difference between a measured screw position at a time when a leading end of a resin flow passes through the resin sensor and a theoretical screw position.

CONSTITUTION: A resin sensor 6 is provided in a resin path 11 of a stationary mold 10a at the top of a nozzle 4. The passing of the leading end of an injected melt resin through the resin sensor 6 is detected by the resin sensor 6. The resin sensor 6 transmits a signal to a controller of an injection molding machine. On reception of the signal, a progressed screw position is measured in a period from the start of injection to the passing of the melt resin through the resin sensor 6. The obtained measured value is compared with a theoretical value in the calculation of operational conditions for the injection stage. If a difference exists, a set value from then is appropriately corrected by the difference. In this manner, a stable action in an injection stage can be embodied.