The objective of the present study is to analyze the relationship of suppliers and customer participation in product development process and effects of such participation on product innovation since it is getting more and more weight in manufacturing companies. It is also aimed in this study to explore if business performance of manufacturing companies might be affected by the suppliers participation as well as product innovation that is realizable by such participation. From the analysis, following conclusions could be drawn: First, suppliers participation in manufacturing companies turned out to have influence upon product innovation (standardized coefficient=0.193, C.R=3.510), implying that nothing is more important than the role of suppliers who have intention to realize innovation through participation in manufacturing companies. Second, the analysis showed that customer participation exercised impact upon product innovation of manufacturing companies (standardized coefficient=0.686, C.R=6.433), suggesting that the more customer participate in product development process of manufacturing companies, the more manufacturing companies could sharpen their competitiveness. Third, it was made known from the analysis that the product innovation thanks to suppliers and customer participation in manufacturing companies could have influence upon their business performance (standardized coefficient=0.762, C.R=7.666), signifying that the product innovation of manufacturing companies might depend on the participation of suppliers and manufacturers and, in turn, could affect their own business performance.