Production condition data and product quality data in a production line are monitored and stored in a production history database. When a quality deterioration event in the production line is detected while checking the product quality data, the improvement contents of the quality deterioration factor and production conditions are extracted. The extracted results and pre-stored quality improvement history data are collated with each other in order to confirm the validity thereof, and a simulation of the phenomenon of the production line is executed in order to verify the correctness. When the validity and correctness are verified, the production condition for the production line are revised to improve the quality deterioration factor.