ABUSTRACTAutomation of production facilities is promoted actively by the automotive industry to save the manpower and to increase productivity. Information networking of production facilities is also promoted rapidly at the plant level, in order to reduce the Production lead time and to upgrade the productivity so that information on customers' orders can be reflected in production, as represented by efforts being made in CIM (Computer Integrated Manufacturing).Needs for a proper information network for individual production system were intensified at Toyota Motor Corporation also, and trial and error were hence repeated. Consequently, it was judged that a broadband Network System would be optimum as a back-bone factory LAN(Local Area Network), which has been introduced into various plants of Toyota consecutively.This paper will introduce reasons for the adoption of the broadband network system and examples of its applications first. Then design policies of Toyota on introduction of the system will be described. Lastly, its operation and administration procedures will be discussed from users' point of view.