The force pushing the ejector pin when a molded product is ejected is obtained from the driving torque of the servomotor. A malfunction is detected in the ejection step as follows. First, a reference pattern is obtained in advance, when a molded product is normally removed. As the reference pattern, the relationship between torque of the servomotor and time from the initiation of ejecting the ejector pin or the position of an ejector pin is used. At least one monitoring zone is set based on the pattern and the upper and lower limits of torque of each of the monitoring zones are set. A torque value is monitored in each monitoring zone and when the torque value falls outside the upper and lower limits of any one of the monitoring zones, it is determined that a malfunction occurred and an alarm is raised.