A system for monitoring the charging performance of a capacitor in an electric circuit in a manufacturing machine installed in a production line includes a charging voltage detecting section for detecting the charging voltage of the capacitor. A control device of the production machine measures, as the charging time, a time from starting charging to a time when a specified charging complete determination voltage that can be used to determine when the charging voltage of the capacitor has reached full charge is reached based on the charging voltage of the capacitor detected by charging voltage detecting section, determines whether the capacitor has deteriorated by determining whether the measured charging time is equal to or less than a specified deterioration threshold value, and upon determining that the capacitor has deteriorated, issues a warning to an operator via a display or sound.