Abstract: A quality control system comprises servers connected to companies having different quality control in-house systems and interconnected through networks and client devices operated by quality control managers belonging to the respective companies. In this quality control system, when the client device of one company logs in a server, according to the definition of the one company as a master and the definition of the customer company (step S1), definition of QPP data including quality information of the one company, product structure information, and production process information (step S2), definition of association of the QPP data of the one company and the customer company (step S3), and integration of the information defined at steps S2, S3(step S4), a quality control information chain linking the companies is formed.