If a screw is moved forward after a metering step is completed, the screw moves in a state where a check ring on a tip end of the screw is in open state. Resin flows in a direction opposite to the injection direction. A rotational force is applied to the screw due to the backflow of the resin. If the check ring closes a resin passage, the rotational force acting on the screw is reduced. A peak time of the screw rotational force is detected as closing point in time of the check ring. Physical amounts such as a screw rotational force and a screw position at that timing are detected. Since the closing point in time of the check ring is precisely detected, correction of the injection/hold pressure switching position and the injection speed switching position can be adjusted more precisely. It is possible to precisely determine whether a molded article is non-defective or defective based on the detected physical amount.