A cellular manufacturing system is good at producing diversified products flexibly; however, its assembly efficiency depends mainly on its operators' abilities. As the workforce shrinks in Japan, cellular manufacturing systems are difficult to maintain. In this case, a new assembly system has been developed since 2006 that combines both the dexterities of human operators and the advantages of automatic machinery. Its characteristics consist of three aspects: collaboration between an operator and twin manipulators on a mobile base, assembly information guidance, and safe design for collaboration. To meet the rapid changing tastes of customers, operators have to assemble various products without longtime training. This requires an effective assembly skill transfer system to extract assembly skills from skilled operators, and then transfer them to novice ones. Considering the characteristics of a cellular manufacturing system, an assembly skill transfer system was proposed and used to extract and transfer assembly skills in both cognition and execution aspects. Taking a cable harness task as an example, the proposed skill transfer system was applied in a developed assembly system. The results show that working under the developed assembly system with physical support, informational support, and the assembly skill transfer system, novice operators' assembly performance was greatly improved. This verified the effect of the proposed solution to maintain the cellular manufacturing system in the aging Japanese society.